Apply default null-safety migrations

lib/models/documents/attribute.dart

@@ -102,46 +102,46 @@ class Attribute<T> {
     Attribute.blockQuote.key,
   };
 
-  static Attribute<int> get h1 => HeaderAttribute(level: 1);
+  static Attribute<int?> get h1 => HeaderAttribute(level: 1);
 
-  static Attribute<int> get h2 => HeaderAttribute(level: 2);
+  static Attribute<int?> get h2 => HeaderAttribute(level: 2);
 
-  static Attribute<int> get h3 => HeaderAttribute(level: 3);
+  static Attribute<int?> get h3 => HeaderAttribute(level: 3);
 
   // "attributes":{"align":"left"}
-  static Attribute<String> get leftAlignment => AlignAttribute('left');
+  static Attribute<String?> get leftAlignment => AlignAttribute('left');
 
   // "attributes":{"align":"center"}
-  static Attribute<String> get centerAlignment => AlignAttribute('center');
+  static Attribute<String?> get centerAlignment => AlignAttribute('center');
 
   // "attributes":{"align":"right"}
-  static Attribute<String> get rightAlignment => AlignAttribute('right');
+  static Attribute<String?> get rightAlignment => AlignAttribute('right');
 
   // "attributes":{"align":"justify"}
-  static Attribute<String> get justifyAlignment => AlignAttribute('justify');
+  static Attribute<String?> get justifyAlignment => AlignAttribute('justify');
 
   // "attributes":{"list":"bullet"}
-  static Attribute<String> get ul => ListAttribute('bullet');
+  static Attribute<String?> get ul => ListAttribute('bullet');
 
   // "attributes":{"list":"ordered"}
-  static Attribute<String> get ol => ListAttribute('ordered');
+  static Attribute<String?> get ol => ListAttribute('ordered');
 
   // "attributes":{"list":"checked"}
-  static Attribute<String> get checked => ListAttribute('checked');
+  static Attribute<String?> get checked => ListAttribute('checked');
 
   // "attributes":{"list":"unchecked"}
-  static Attribute<String> get unchecked => ListAttribute('unchecked');
+  static Attribute<String?> get unchecked => ListAttribute('unchecked');
 
   // "attributes":{"indent":1"}
-  static Attribute<int> get indentL1 => IndentAttribute(level: 1);
+  static Attribute<int?> get indentL1 => IndentAttribute(level: 1);
 
   // "attributes":{"indent":2"}
-  static Attribute<int> get indentL2 => IndentAttribute(level: 2);
+  static Attribute<int?> get indentL2 => IndentAttribute(level: 2);
 
   // "attributes":{"indent":3"}
-  static Attribute<int> get indentL3 => IndentAttribute(level: 3);
+  static Attribute<int?> get indentL3 => IndentAttribute(level: 3);
 
-  static Attribute<int> getIndentLevel(int level) {
+  static Attribute<int?> getIndentLevel(int? level) {
     if (level == 1) {
       return indentL1;
     }
@@ -161,7 +161,7 @@ class Attribute<T> {
     if (!_registry.containsKey(key)) {
       throw ArgumentError.value(key, 'key "$key" not found.');
     }
-    Attribute origin = _registry[key];
+    Attribute origin = _registry[key]!;
     Attribute attribute = clone(origin, value);
     return attribute;
   }
@@ -205,24 +205,24 @@ class StrikeThroughAttribute extends Attribute<bool> {
   StrikeThroughAttribute() : super('strike', AttributeScope.INLINE, true);
 }
 
-class FontAttribute extends Attribute<String> {
+class FontAttribute extends Attribute<String?> {
-  FontAttribute(String val) : super('font', AttributeScope.INLINE, val);
+  FontAttribute(String? val) : super('font', AttributeScope.INLINE, val);
 }
 
-class SizeAttribute extends Attribute<String> {
+class SizeAttribute extends Attribute<String?> {
-  SizeAttribute(String val) : super('size', AttributeScope.INLINE, val);
+  SizeAttribute(String? val) : super('size', AttributeScope.INLINE, val);
 }
 
-class LinkAttribute extends Attribute<String> {
+class LinkAttribute extends Attribute<String?> {
-  LinkAttribute(String val) : super('link', AttributeScope.INLINE, val);
+  LinkAttribute(String? val) : super('link', AttributeScope.INLINE, val);
 }
 
-class ColorAttribute extends Attribute<String> {
+class ColorAttribute extends Attribute<String?> {
-  ColorAttribute(String val) : super('color', AttributeScope.INLINE, val);
+  ColorAttribute(String? val) : super('color', AttributeScope.INLINE, val);
 }
 
-class BackgroundAttribute extends Attribute<String> {
+class BackgroundAttribute extends Attribute<String?> {
-  BackgroundAttribute(String val)
+  BackgroundAttribute(String? val)
       : super('background', AttributeScope.INLINE, val);
 }
 
@@ -231,20 +231,20 @@ class PlaceholderAttribute extends Attribute<bool> {
   PlaceholderAttribute() : super('placeholder', AttributeScope.INLINE, true);
 }
 
-class HeaderAttribute extends Attribute<int> {
+class HeaderAttribute extends Attribute<int?> {
-  HeaderAttribute({int level}) : super('header', AttributeScope.BLOCK, level);
+  HeaderAttribute({int? level}) : super('header', AttributeScope.BLOCK, level);
 }
 
-class IndentAttribute extends Attribute<int> {
+class IndentAttribute extends Attribute<int?> {
-  IndentAttribute({int level}) : super('indent', AttributeScope.BLOCK, level);
+  IndentAttribute({int? level}) : super('indent', AttributeScope.BLOCK, level);
 }
 
-class AlignAttribute extends Attribute<String> {
+class AlignAttribute extends Attribute<String?> {
-  AlignAttribute(String val) : super('align', AttributeScope.BLOCK, val);
+  AlignAttribute(String? val) : super('align', AttributeScope.BLOCK, val);
 }
 
-class ListAttribute extends Attribute<String> {
+class ListAttribute extends Attribute<String?> {
-  ListAttribute(String val) : super('list', AttributeScope.BLOCK, val);
+  ListAttribute(String? val) : super('list', AttributeScope.BLOCK, val);
 }
 
 class CodeBlockAttribute extends Attribute<bool> {
@@ -255,14 +255,14 @@ class BlockQuoteAttribute extends Attribute<bool> {
   BlockQuoteAttribute() : super('blockquote', AttributeScope.BLOCK, true);
 }
 
-class WidthAttribute extends Attribute<String> {
+class WidthAttribute extends Attribute<String?> {
-  WidthAttribute(String val) : super('width', AttributeScope.IGNORE, val);
+  WidthAttribute(String? val) : super('width', AttributeScope.IGNORE, val);
 }
 
-class HeightAttribute extends Attribute<String> {
+class HeightAttribute extends Attribute<String?> {
-  HeightAttribute(String val) : super('height', AttributeScope.IGNORE, val);
+  HeightAttribute(String? val) : super('height', AttributeScope.IGNORE, val);
 }
 
-class StyleAttribute extends Attribute<String> {
+class StyleAttribute extends Attribute<String?> {
-  StyleAttribute(String val) : super('style', AttributeScope.IGNORE, val);
+  StyleAttribute(String? val) : super('style', AttributeScope.IGNORE, val);
 }

lib/models/documents/document.dart

@@ -43,11 +43,11 @@ class Document {
     _loadDocument(_delta);
   }
 
-  Delta insert(int index, Object data) {
+  Delta insert(int index, Object? data) {
     assert(index >= 0);
     assert(data is String || data is Embeddable);
     if (data is Embeddable) {
-      data = (data as Embeddable).toJson();
+      data = data.toJson();
     } else if ((data as String).isEmpty) {
       return Delta();
     }
@@ -66,7 +66,7 @@ class Document {
     return delta;
   }
 
-  Delta replace(int index, int len, Object data) {
+  Delta replace(int index, int len, Object? data) {
     assert(index >= 0);
     assert(data is String || data is Embeddable);
 
@@ -88,7 +88,7 @@ class Document {
     return delta;
   }
 
-  Delta format(int index, int len, Attribute attribute) {
+  Delta format(int index, int len, Attribute? attribute) {
     assert(index >= 0 && len >= 0 && attribute != null);
 
     Delta delta = Delta();
@@ -113,7 +113,7 @@ class Document {
     if (res.node is Line) {
       return res;
     }
-    Block block = res.node;
+    Block block = res.node as Block;
     return block.queryChild(res.offset, true);
   }
 
@@ -126,7 +126,7 @@ class Document {
     delta = _transform(delta);
     Delta originalDelta = toDelta();
     for (Operation op in delta.toList()) {
-      Style style =
+      Style? style =
           op.attributes != null ? Style.fromJson(op.attributes) : null;
 
       if (op.isInsert) {
@@ -138,7 +138,7 @@ class Document {
       }
 
       if (!op.isDelete) {
-        offset += op.length;
+        offset += op.length!;
       }
     }
     try {
@@ -197,7 +197,7 @@ class Document {
     }
   }
 
-  Object _normalize(Object data) {
+  Object _normalize(Object? data) {
     if (data is String) {
       return data;
     }
@@ -205,7 +205,7 @@ class Document {
     if (data is Embeddable) {
       return data;
     }
-    return Embeddable.fromJson(data);
+    return Embeddable.fromJson(data as Map<String, dynamic>);
   }
 
   close() {
@@ -227,7 +227,7 @@ class Document {
           op.attributes != null ? Style.fromJson(op.attributes) : null;
       final data = _normalize(op.data);
       _root.insert(offset, data, style);
-      offset += op.length;
+      offset += op.length!;
     }
     final node = _root.last;
     if (node is Line &&

lib/models/documents/history.dart

@@ -90,13 +90,13 @@ class History {
     }
     Delta delta = source.removeLast();
     // look for insert or delete
-    int len = 0;
+    int? len = 0;
     List<Operation> ops = delta.toList();
     for (var i = 0; i < ops.length; i++) {
       if (ops[i].key == Operation.insertKey) {
         len = ops[i].length;
       } else if (ops[i].key == Operation.deleteKey) {
-        len = ops[i].length * -1;
+        len = ops[i].length! * -1;
       }
     }
     Delta base = Delta.from(doc.toDelta());

lib/models/documents/nodes/block.dart

@@ -4,7 +4,7 @@ import 'container.dart';
 import 'line.dart';
 import 'node.dart';
 
-class Block extends Container<Line> {
+class Block extends Container<Line?> {
   @override
   Line get defaultChild => Line();
 
@@ -18,7 +18,7 @@ class Block extends Container<Line> {
   @override
   adjust() {
     if (isEmpty) {
-      Node sibling = previous;
+      Node? sibling = previous;
       unlink();
       if (sibling != null) {
         sibling.adjust();
@@ -27,18 +27,18 @@ class Block extends Container<Line> {
     }
 
     Block block = this;
-    Node prev = block.previous;
+    Node? prev = block.previous;
     // merging it with previous block if style is the same
     if (!block.isFirst &&
         block.previous is Block &&
-        prev.style == block.style) {
+        prev!.style == block.style) {
-      block.moveChildToNewParent(prev);
+      block.moveChildToNewParent(prev as Container<Node?>?);
       block.unlink();
-      block = prev;
+      block = prev as Block;
     }
-    Node next = block.next;
+    Node? next = block.next;
     // merging it with next block if style is the same
-    if (!block.isLast && block.next is Block && next.style == block.style) {
+    if (!block.isLast && block.next is Block && next!.style == block.style) {
       (next as Block).moveChildToNewParent(block);
       next.unlink();
     }

lib/models/documents/nodes/container.dart

@@ -4,7 +4,7 @@ import '../style.dart';
 import 'node.dart';
 
 /* Container of multiple nodes */
-abstract class Container<T extends Node> extends Node {
+abstract class Container<T extends Node?> extends Node {
   final LinkedList<Node> _children = LinkedList<Node>();
 
   LinkedList<Node> get children => _children;
@@ -26,32 +26,32 @@ abstract class Container<T extends Node> extends Node {
   /// abstract methods end
 
   add(T node) {
-    assert(node.parent == null);
+    assert(node?.parent == null);
-    node.parent = this;
+    node?.parent = this;
-    _children.add(node);
+    _children.add(node!);
   }
 
   addFirst(T node) {
-    assert(node.parent == null);
+    assert(node?.parent == null);
-    node.parent = this;
+    node?.parent = this;
-    _children.addFirst(node);
+    _children.addFirst(node!);
   }
 
   void remove(T node) {
-    assert(node.parent == this);
+    assert(node?.parent == this);
-    node.parent = null;
+    node?.parent = null;
-    _children.remove(node);
+    _children.remove(node!);
   }
 
-  void moveChildToNewParent(Container newParent) {
+  void moveChildToNewParent(Container? newParent) {
     if (isEmpty) {
       return;
     }
 
-    T last = newParent.isEmpty ? null : newParent.last;
+    T? last = newParent!.isEmpty ? null : newParent.last as T?;
     while (isNotEmpty) {
-      T child = first;
+      T child = first as T;
-      child.unlink();
+      child?.unlink();
       newParent.add(child);
     }
 
@@ -80,12 +80,12 @@ abstract class Container<T extends Node> extends Node {
   int get length => _children.fold(0, (cur, node) => cur + node.length);
 
   @override
-  insert(int index, Object data, Style style) {
+  insert(int index, Object data, Style? style) {
     assert(index == 0 || (index > 0 && index < length));
 
     if (isNotEmpty) {
       ChildQuery child = queryChild(index, false);
-      child.node.insert(child.offset, data, style);
+      child.node!.insert(child.offset, data, style);
       return;
     }
 
@@ -93,21 +93,21 @@ abstract class Container<T extends Node> extends Node {
     assert(index == 0);
     T node = defaultChild;
     add(node);
-    node.insert(index, data, style);
+    node?.insert(index, data, style);
   }
 
   @override
-  retain(int index, int length, Style attributes) {
+  retain(int index, int? length, Style? attributes) {
     assert(isNotEmpty);
     ChildQuery child = queryChild(index, false);
-    child.node.retain(child.offset, length, attributes);
+    child.node!.retain(child.offset, length, attributes);
   }
 
   @override
-  delete(int index, int length) {
+  delete(int index, int? length) {
     assert(isNotEmpty);
     ChildQuery child = queryChild(index, false);
-    child.node.delete(child.offset, length);
+    child.node!.delete(child.offset, length);
   }
 
   @override
@@ -116,7 +116,7 @@ abstract class Container<T extends Node> extends Node {
 
 /// Query of a child in a Container
 class ChildQuery {
-  final Node node; // null if not found
+  final Node? node; // null if not found
 
   final int offset;
 

lib/models/documents/nodes/leaf.dart

@@ -13,13 +13,9 @@ abstract class Leaf extends Node {
 
   Object get value => _value;
 
-  Leaf.val(Object val)
+  Leaf.val(Object val) : _value = val;
-      : assert(val != null),
-        _value = val;
-
-  factory Leaf([Object data]) {
-    assert(data != null);
 
+  factory Leaf(Object data) {
     if (data is Embeddable) {
       return Embed(data);
     }
@@ -37,7 +33,7 @@ abstract class Leaf extends Node {
   }
 
   @override
-  Line get parent => super.parent as Line;
+  Line? get parent => super.parent as Line?;
 
   @override
   int get length {
@@ -55,11 +51,11 @@ abstract class Leaf extends Node {
   }
 
   @override
-  insert(int index, Object data, Style style) {
+  insert(int index, Object data, Style? style) {
     assert(data != null && index >= 0 && index <= length);
     Leaf node = Leaf(data);
     if (index < length) {
-      splitAt(index).insertBefore(node);
+      splitAt(index)!.insertBefore(node);
     } else {
       insertAfter(node);
     }
@@ -67,36 +63,36 @@ abstract class Leaf extends Node {
   }
 
   @override
-  retain(int index, int len, Style style) {
+  retain(int index, int? len, Style? style) {
     if (style == null) {
       return;
     }
 
-    int local = math.min(this.length - index, len);
+    int local = math.min(this.length - index, len!);
     int remain = len - local;
     Leaf node = _isolate(index, local);
 
     if (remain > 0) {
       assert(node.next != null);
-      node.next.retain(0, remain, style);
+      node.next!.retain(0, remain, style);
     }
     node.format(style);
   }
 
   @override
-  delete(int index, int len) {
+  delete(int index, int? len) {
     assert(index < this.length);
 
-    int local = math.min(this.length - index, len);
+    int local = math.min(this.length - index, len!);
     Leaf target = _isolate(index, local);
-    Leaf prev = target.previous;
+    Leaf? prev = target.previous as Leaf?;
-    Leaf next = target.next;
+    Leaf? next = target.next as Leaf?;
     target.unlink();
 
     int remain = len - local;
     if (remain > 0) {
       assert(next != null);
-      next.delete(0, remain);
+      next!.delete(0, remain);
     }
 
     if (prev != null) {
@@ -112,7 +108,7 @@ abstract class Leaf extends Node {
 
     Text node = this as Text;
     // merging it with previous node if style is the same
-    Node prev = node.previous;
+    Node? prev = node.previous;
     if (!node.isFirst && prev is Text && prev.style == node.style) {
       prev._value = prev.value + node.value;
       node.unlink();
@@ -120,27 +116,27 @@ abstract class Leaf extends Node {
     }
 
     // merging it with next node if style is the same
-    Node next = node.next;
+    Node? next = node.next;
     if (!node.isLast && next is Text && next.style == node.style) {
       node._value = node.value + next.value;
       next.unlink();
     }
   }
 
-  Leaf cutAt(int index) {
+  Leaf? cutAt(int index) {
     assert(index >= 0 && index <= length);
-    Leaf cut = splitAt(index);
+    Leaf? cut = splitAt(index);
     cut?.unlink();
     return cut;
   }
 
-  Leaf splitAt(int index) {
+  Leaf? splitAt(int index) {
     assert(index >= 0 && index <= length);
     if (index == 0) {
       return this;
     }
     if (index == length) {
-      return isLast ? null : next as Leaf;
+      return isLast ? null : next as Leaf?;
     }
 
     assert(this is Text);
@@ -152,7 +148,7 @@ abstract class Leaf extends Node {
     return split;
   }
 
-  format(Style style) {
+  format(Style? style) {
     if (style != null && style.isNotEmpty) {
       applyStyle(style);
     }
@@ -163,7 +159,7 @@ abstract class Leaf extends Node {
   Leaf _isolate(int index, int length) {
     assert(
         index >= 0 && index < this.length && (index + length <= this.length));
-    Leaf target = splitAt(index);
+    Leaf target = splitAt(index)!;
     target.splitAt(length);
     return target;
   }

lib/models/documents/nodes/line.dart

@@ -10,7 +10,7 @@ import 'container.dart';
 import 'embed.dart';
 import 'leaf.dart';
 
-class Line extends Container<Leaf> {
+class Line extends Container<Leaf?> {
   @override
   Leaf get defaultChild => Text();
 
@@ -25,28 +25,28 @@ class Line extends Container<Leaf> {
     return children.single is Embed;
   }
 
-  Line get nextLine {
+  Line? get nextLine {
     if (!isLast) {
-      return next is Block ? (next as Block).first : next;
+      return next is Block ? (next as Block).first as Line? : next as Line?;
     }
     if (parent is! Block) {
       return null;
     }
 
-    if (parent.isLast) {
+    if (parent!.isLast) {
       return null;
     }
-    return parent.next is Block ? (parent.next as Block).first : parent.next;
+    return parent!.next is Block ? (parent!.next as Block).first as Line? : parent!.next as Line?;
   }
 
   @override
   Delta toDelta() {
     final delta = children
         .map((child) => child.toDelta())
-        .fold(Delta(), (a, b) => a.concat(b));
+        .fold(Delta(), (dynamic a, b) => a.concat(b));
     var attributes = style;
     if (parent is Block) {
-      Block block = parent;
+      Block block = parent as Block;
       attributes = attributes.mergeAll(block.style);
     }
     delta.insert('\n', attributes.toJson());
@@ -64,7 +64,7 @@ class Line extends Container<Leaf> {
   }
 
   @override
-  insert(int index, Object data, Style style) {
+  insert(int index, Object data, Style? style) {
     if (data is Embeddable) {
       _insert(index, data, style);
       return;
@@ -99,13 +99,13 @@ class Line extends Container<Leaf> {
   }
 
   @override
-  retain(int index, int len, Style style) {
+  retain(int index, int? len, Style? style) {
     if (style == null) {
       return;
     }
     int thisLen = this.length;
 
-    int local = math.min(thisLen - index, len);
+    int local = math.min(thisLen - index, len!);
 
     if (index + local == thisLen && local == 1) {
       assert(style.values.every((attr) => attr.scope == AttributeScope.BLOCK));
@@ -119,13 +119,13 @@ class Line extends Container<Leaf> {
     int remain = len - local;
     if (remain > 0) {
       assert(nextLine != null);
-      nextLine.retain(0, remain, style);
+      nextLine!.retain(0, remain, style);
     }
   }
 
   @override
-  delete(int index, int len) {
+  delete(int index, int? len) {
-    int local = math.min(this.length - index, len);
+    int local = math.min(this.length - index, len!);
     bool deleted = index + local == this.length;
     if (deleted) {
       clearStyle();
@@ -139,35 +139,35 @@ class Line extends Container<Leaf> {
     int remain = len - local;
     if (remain > 0) {
       assert(nextLine != null);
-      nextLine.delete(0, remain);
+      nextLine!.delete(0, remain);
     }
 
     if (deleted && isNotEmpty) {
       assert(nextLine != null);
-      nextLine.moveChildToNewParent(this);
+      nextLine!.moveChildToNewParent(this);
       moveChildToNewParent(nextLine);
     }
 
     if (deleted) {
-      Node p = parent;
+      Node p = parent!;
       unlink();
       p.adjust();
     }
   }
 
-  void _format(Style newStyle) {
+  void _format(Style? newStyle) {
     if (newStyle == null || newStyle.isEmpty) {
       return;
     }
 
     applyStyle(newStyle);
-    Attribute blockStyle = newStyle.getBlockExceptHeader();
+    Attribute? blockStyle = newStyle.getBlockExceptHeader();
     if (blockStyle == null) {
       return;
     }
 
     if (parent is Block) {
-      Attribute parentStyle = (parent as Block).style.getBlockExceptHeader();
+      Attribute? parentStyle = (parent as Block).style.getBlockExceptHeader();
       if (blockStyle.value == null) {
         _unwrap();
       } else if (blockStyle != parentStyle) {
@@ -196,7 +196,7 @@ class Line extends Container<Leaf> {
     if (parent is! Block) {
       throw ArgumentError('Invalid parent');
     }
-    Block block = parent;
+    Block block = parent as Block;
 
     assert(block.children.contains(this));
 
@@ -207,10 +207,10 @@ class Line extends Container<Leaf> {
       unlink();
       block.insertAfter(this);
     } else {
-      Block before = block.clone();
+      Block before = block.clone() as Block;
       block.insertBefore(before);
 
-      Line child = block.first;
+      Line child = block.first as Line;
       while (child != this) {
         child.unlink();
         before.add(child);
@@ -232,19 +232,19 @@ class Line extends Container<Leaf> {
     }
 
     ChildQuery query = queryChild(index, false);
-    while (!query.node.isLast) {
+    while (!query.node!.isLast) {
-      Leaf next = last;
+      Leaf next = last as Leaf;
       next.unlink();
       line.addFirst(next);
     }
-    Leaf child = query.node;
+    Leaf child = query.node as Leaf;
-    Leaf cut = child.splitAt(query.offset);
+    Leaf? cut = child.splitAt(query.offset);
     cut?.unlink();
     line.addFirst(cut);
     return line;
   }
 
-  _insert(int index, Object data, Style style) {
+  _insert(int index, Object data, Style? style) {
     assert(index == 0 || (index > 0 && index < length));
 
     if (data is String) {
@@ -256,7 +256,7 @@ class Line extends Container<Leaf> {
 
     if (isNotEmpty) {
       ChildQuery result = queryChild(index, true);
-      result.node.insert(result.offset, data, style);
+      result.node!.insert(result.offset, data, style);
       return;
     }
 
@@ -291,26 +291,26 @@ class Line extends Container<Leaf> {
     }
 
     ChildQuery data = queryChild(offset, true);
-    Leaf node = data.node;
+    Leaf? node = data.node as Leaf?;
     if (node != null) {
       res = res.mergeAll(node.style);
       int pos = node.length - data.offset;
-      while (!node.isLast && pos < local) {
+      while (!node!.isLast && pos < local) {
-        node = node.next as Leaf;
+        node = node.next as Leaf?;
-        _handle(node.style);
+        _handle(node!.style);
         pos += node.length;
       }
     }
 
     res = res.mergeAll(style);
     if (parent is Block) {
-      Block block = parent;
+      Block block = parent as Block;
       res = res.mergeAll(block.style);
     }
 
     int remain = len - local;
     if (remain > 0) {
-      _handle(nextLine.collectStyle(0, remain));
+      _handle(nextLine!.collectStyle(0, remain));
     }
 
     return res;

lib/models/documents/nodes/node.dart

@@ -9,7 +9,7 @@ import 'line.dart';
 
 /* node in a document tree */
 abstract class Node extends LinkedListEntry<Node> {
-  Container parent;
+  Container? parent;
   Style _style = Style();
 
   Style get style => _style;
@@ -29,9 +29,9 @@ abstract class Node extends LinkedListEntry<Node> {
     _style = Style();
   }
 
-  bool get isFirst => list.first == this;
+  bool get isFirst => list!.first == this;
 
-  bool get isLast => list.last == this;
+  bool get isLast => list!.last == this;
 
   int get length;
 
@@ -50,14 +50,14 @@ abstract class Node extends LinkedListEntry<Node> {
 
     Node cur = this;
     do {
-      cur = cur.previous;
+      cur = cur.previous!;
       offset += cur.length;
     } while (!cur.isFirst);
     return offset;
   }
 
   int getDocumentOffset() {
-    final parentOffset = (parent is! Root) ? parent.getDocumentOffset() : 0;
+    final parentOffset = (parent is! Root) ? parent!.getDocumentOffset() : 0;
     return parentOffset + getOffset();
   }
 
@@ -99,20 +99,20 @@ abstract class Node extends LinkedListEntry<Node> {
 
   Delta toDelta();
 
-  insert(int index, Object data, Style style);
+  insert(int index, Object data, Style? style);
 
-  retain(int index, int len, Style style);
+  retain(int index, int? len, Style? style);
 
-  delete(int index, int len);
+  delete(int index, int? len);
 
   /// abstract methods end
 
 }
 
 /* Root node of document tree */
-class Root extends Container<Container<Node>> {
+class Root extends Container<Container<Node?>> {
   @override
-  Container<Node> get defaultChild => Line();
+  Container<Node?> get defaultChild => Line();
 
   @override
   Delta toDelta() => children

lib/models/documents/style.dart

@@ -10,7 +10,7 @@ class Style {
 
   Style() : _attributes = <String, Attribute>{};
 
-  static Style fromJson(Map<String, dynamic> attributes) {
+  static Style fromJson(Map<String, dynamic>? attributes) {
     if (attributes == null) {
       return Style();
     }
@@ -22,7 +22,7 @@ class Style {
     return Style.attr(result);
   }
 
-  Map<String, dynamic> toJson() => _attributes.isEmpty
+  Map<String, dynamic>? toJson() => _attributes.isEmpty
       ? null
       : _attributes.map<String, dynamic>((String _, Attribute attribute) =>
           MapEntry<String, dynamic>(attribute.key, attribute.value));
@@ -46,7 +46,7 @@ class Style {
 
   bool containsKey(String key) => _attributes.containsKey(key);
 
-  Attribute getBlockExceptHeader() {
+  Attribute? getBlockExceptHeader() {
     for (Attribute val in values) {
       if (val.isBlockExceptHeader) {
         return val;

lib/models/quill_delta.dart

@@ -15,10 +15,10 @@ const _valueEquality = DeepCollectionEquality();
 /// Decoder function to convert raw `data` object into a user-defined data type.
 ///
 /// Useful with embedded content.
-typedef DataDecoder = Object Function(Object data);
+typedef DataDecoder = Object? Function(Object data);
 
 /// Default data decoder which simply passes through the original value.
-Object _passThroughDataDecoder(Object data) => data;
+Object? _passThroughDataDecoder(Object? data) => data;
 
 /// Operation performed on a rich-text document.
 class Operation {
@@ -40,17 +40,17 @@ class Operation {
   final String key;
 
   /// Length of this operation.
-  final int length;
+  final int? length;
 
   /// Payload of "insert" operation, for other types is set to empty string.
-  final Object data;
+  final Object? data;
 
   /// Rich-text attributes set by this operation, can be `null`.
-  Map<String, dynamic> get attributes =>
+  Map<String, dynamic>? get attributes =>
-      _attributes == null ? null : Map<String, dynamic>.from(_attributes);
+      _attributes == null ? null : Map<String, dynamic>.from(_attributes!);
-  final Map<String, dynamic> _attributes;
+  final Map<String, dynamic>? _attributes;
 
-  Operation._(this.key, this.length, this.data, Map attributes)
+  Operation._(this.key, this.length, this.data, Map? attributes)
       : assert(key != null && length != null && data != null),
         assert(_validKeys.contains(key), 'Invalid operation key "$key".'),
         assert(() {
@@ -64,7 +64,7 @@ class Operation {
   ///
   /// If `dataDecoder` parameter is not null then it is used to additionally
   /// decode the operation's data object. Only applied to insert operations.
-  static Operation fromJson(Map data, {DataDecoder dataDecoder}) {
+  static Operation fromJson(Map data, {DataDecoder? dataDecoder}) {
     dataDecoder ??= _passThroughDataDecoder;
     final map = Map<String, dynamic>.from(data);
     if (map.containsKey(Operation.insertKey)) {
@@ -73,10 +73,10 @@ class Operation {
       return Operation._(
           Operation.insertKey, dataLength, data, map[Operation.attributesKey]);
     } else if (map.containsKey(Operation.deleteKey)) {
-      final int length = map[Operation.deleteKey];
+      final int? length = map[Operation.deleteKey];
       return Operation._(Operation.deleteKey, length, '', null);
     } else if (map.containsKey(Operation.retainKey)) {
-      final int length = map[Operation.retainKey];
+      final int? length = map[Operation.retainKey];
       return Operation._(
           Operation.retainKey, length, '', map[Operation.attributesKey]);
     }
@@ -95,13 +95,13 @@ class Operation {
       Operation._(Operation.deleteKey, length, '', null);
 
   /// Creates operation which inserts [text] with optional [attributes].
-  factory Operation.insert(dynamic data, [Map<String, dynamic> attributes]) =>
+  factory Operation.insert(dynamic data, [Map<String, dynamic>? attributes]) =>
       Operation._(Operation.insertKey, data is String ? data.length : 1, data,
           attributes);
 
   /// Creates operation which retains [length] of characters and optionally
   /// applies attributes.
-  factory Operation.retain(int length, [Map<String, dynamic> attributes]) =>
+  factory Operation.retain(int? length, [Map<String, dynamic>? attributes]) =>
       Operation._(Operation.retainKey, length, '', attributes);
 
   /// Returns value of this operation.
@@ -119,7 +119,7 @@ class Operation {
   bool get isRetain => key == Operation.retainKey;
 
   /// Returns `true` if this operation has no attributes, e.g. is plain text.
-  bool get isPlain => (_attributes == null || _attributes.isEmpty);
+  bool get isPlain => (_attributes == null || _attributes!.isEmpty);
 
   /// Returns `true` if this operation sets at least one attribute.
   bool get isNotPlain => !isPlain;
@@ -130,7 +130,7 @@ class Operation {
   bool get isEmpty => length == 0;
 
   /// Returns `true` is this operation is not empty.
-  bool get isNotEmpty => length > 0;
+  bool get isNotEmpty => length! > 0;
 
   @override
   bool operator ==(other) {
@@ -144,7 +144,7 @@ class Operation {
   }
 
   /// Returns `true` if this operation has attribute specified by [name].
-  bool hasAttribute(String name) => isNotPlain && _attributes.containsKey(name);
+  bool hasAttribute(String name) => isNotPlain && _attributes!.containsKey(name);
 
   /// Returns `true` if [other] operation has the same attributes as this one.
   bool hasSameAttributes(Operation other) {
@@ -153,9 +153,9 @@ class Operation {
 
   @override
   int get hashCode {
-    if (_attributes != null && _attributes.isNotEmpty) {
+    if (_attributes != null && _attributes!.isNotEmpty) {
       final attrsHash =
-          hashObjects(_attributes.entries.map((e) => hash2(e.key, e.value)));
+          hashObjects(_attributes!.entries.map((e) => hash2(e.key, e.value)));
       return hash3(key, value, attrsHash);
     }
     return hash2(key, value);
@@ -181,8 +181,8 @@ class Operation {
 /// it is a "change delta".
 class Delta {
   /// Transforms two attribute sets.
-  static Map<String, dynamic> transformAttributes(
+  static Map<String, dynamic>? transformAttributes(
-      Map<String, dynamic> a, Map<String, dynamic> b, bool priority) {
+      Map<String, dynamic>? a, Map<String, dynamic>? b, bool priority) {
     if (a == null) return b;
     if (b == null) return null;
 
@@ -197,8 +197,8 @@ class Delta {
   }
 
   /// Composes two attribute sets.
-  static Map<String, dynamic> composeAttributes(
+  static Map<String, dynamic>? composeAttributes(
-      Map<String, dynamic> a, Map<String, dynamic> b,
+      Map<String, dynamic>? a, Map<String, dynamic>? b,
       {bool keepNull = false}) {
     a ??= const {};
     b ??= const {};
@@ -217,12 +217,12 @@ class Delta {
 
   ///get anti-attr result base on base
   static Map<String, dynamic> invertAttributes(
-      Map<String, dynamic> attr, Map<String, dynamic> base) {
+      Map<String, dynamic>? attr, Map<String, dynamic>? base) {
     attr ??= const {};
     base ??= const {};
 
-    var baseInverted = base.keys.fold({}, (memo, key) {
+    var baseInverted = base.keys.fold({}, (dynamic memo, key) {
-      if (base[key] != attr[key] && attr.containsKey(key)) {
+      if (base![key] != attr![key] && attr.containsKey(key)) {
         memo[key] = base[key];
       }
       return memo;
@@ -230,7 +230,7 @@ class Delta {
 
     var inverted =
         Map<String, dynamic>.from(attr.keys.fold(baseInverted, (memo, key) {
-      if (base[key] != attr[key] && !base.containsKey(key)) {
+      if (base![key] != attr![key] && !base.containsKey(key)) {
         memo[key] = null;
       }
       return memo;
@@ -257,7 +257,7 @@ class Delta {
   ///
   /// If `dataDecoder` parameter is not null then it is used to additionally
   /// decode the operation's data object. Only applied to insert operations.
-  static Delta fromJson(List data, {DataDecoder dataDecoder}) {
+  static Delta fromJson(List data, {DataDecoder? dataDecoder}) {
     return Delta._(data
         .map((op) => Operation.fromJson(op, dataDecoder: dataDecoder))
         .toList());
@@ -304,14 +304,14 @@ class Delta {
   int get hashCode => hashObjects(_operations);
 
   /// Retain [count] of characters from current position.
-  void retain(int count, [Map<String, dynamic> attributes]) {
+  void retain(int count, [Map<String, dynamic>? attributes]) {
     assert(count >= 0);
     if (count == 0) return; // no-op
     push(Operation.retain(count, attributes));
   }
 
   /// Insert [data] at current position.
-  void insert(dynamic data, [Map<String, dynamic> attributes]) {
+  void insert(dynamic data, [Map<String, dynamic>? attributes]) {
     assert(data != null);
     if (data is String && data.isEmpty) return; // no-op
     push(Operation.insert(data, attributes));
@@ -329,7 +329,7 @@ class Delta {
     assert(operation != null && last.key == operation.key);
     assert(operation.data is String && last.data is String);
 
-    final length = operation.length + last.length;
+    final length = operation.length! + last.length!;
     final lastText = last.data as String;
     final opText = operation.data as String;
     final resultText = lastText + opText;
@@ -396,12 +396,12 @@ class Delta {
   /// Returns new operation or `null` if operations from [thisIter] and
   /// [otherIter] nullify each other. For instance, for the pair `insert('abc')`
   /// and `delete(3)` composition result would be empty string.
-  Operation _composeOperation(DeltaIterator thisIter, DeltaIterator otherIter) {
+  Operation? _composeOperation(DeltaIterator thisIter, DeltaIterator otherIter) {
     if (otherIter.isNextInsert) return otherIter.next();
     if (thisIter.isNextDelete) return thisIter.next();
 
     final length = math.min(thisIter.peekLength(), otherIter.peekLength());
-    final thisOp = thisIter.next(length);
+    final thisOp = thisIter.next(length as int);
     final otherOp = otherIter.next(length);
     assert(thisOp.length == otherOp.length);
 
@@ -448,7 +448,7 @@ class Delta {
   /// [thisIter].
   ///
   /// Returns `null` if both operations nullify each other.
-  Operation _transformOperation(
+  Operation? _transformOperation(
       DeltaIterator thisIter, DeltaIterator otherIter, bool priority) {
     if (thisIter.isNextInsert && (priority || !otherIter.isNextInsert)) {
       return Operation.retain(thisIter.next().length);
@@ -457,7 +457,7 @@ class Delta {
     }
 
     final length = math.min(thisIter.peekLength(), otherIter.peekLength());
-    final thisOp = thisIter.next(length);
+    final thisOp = thisIter.next(length as int);
     final otherOp = otherIter.next(length);
     assert(thisOp.length == otherOp.length);
 
@@ -520,12 +520,12 @@ class Delta {
     var baseIndex = 0;
     for (final op in _operations) {
       if (op.isInsert) {
-        inverted.delete(op.length);
+        inverted.delete(op.length!);
       } else if (op.isRetain && op.isPlain) {
-        inverted.retain(op.length, null);
+        inverted.retain(op.length!, null);
-        baseIndex += op.length;
+        baseIndex += op.length!;
       } else if (op.isDelete || (op.isRetain && op.isNotPlain)) {
-        final length = op.length;
+        final length = op.length!;
         final sliceDelta = base.slice(baseIndex, baseIndex + length);
         sliceDelta.toList().forEach((baseOp) {
           if (op.isDelete) {
@@ -533,7 +533,7 @@ class Delta {
           } else if (op.isRetain && op.isNotPlain) {
             var invertAttr = invertAttributes(op.attributes, baseOp.attributes);
             inverted.retain(
-                baseOp.length, invertAttr.isEmpty ? null : invertAttr);
+                baseOp.length!, invertAttr.isEmpty ? null : invertAttr);
           }
         });
         baseIndex += length;
@@ -547,7 +547,7 @@ class Delta {
 
   /// Returns slice of this delta from [start] index (inclusive) to [end]
   /// (exclusive).
-  Delta slice(int start, [int end]) {
+  Delta slice(int start, [int? end]) {
     final delta = Delta();
     var index = 0;
     var opIterator = DeltaIterator(this);
@@ -559,10 +559,10 @@ class Delta {
       if (index < start) {
         op = opIterator.next(start - index);
       } else {
-        op = opIterator.next(actualEnd - index);
+        op = opIterator.next(actualEnd - index as int);
         delta.push(op);
       }
-      index += op.length;
+      index += op.length!;
     }
     return delta;
   }
@@ -585,12 +585,12 @@ class Delta {
     while (iter.hasNext && offset <= index) {
       final op = iter.next();
       if (op.isDelete) {
-        index -= math.min(op.length, index - offset);
+        index -= math.min(op.length!, index - offset);
         continue;
       } else if (op.isInsert && (offset < index || force)) {
-        index += op.length;
+        index += op.length!;
       }
-      offset += op.length;
+      offset += op.length!;
     }
     return index;
   }
@@ -614,7 +614,7 @@ class DeltaIterator {
 
   bool get isNextRetain => nextOperationKey == Operation.retainKey;
 
-  String get nextOperationKey {
+  String? get nextOperationKey {
     if (_index < delta.length) {
       return delta.elementAt(_index).key;
     } else {
@@ -630,7 +630,7 @@ class DeltaIterator {
   num peekLength() {
     if (_index < delta.length) {
       final operation = delta._operations[_index];
-      return operation.length - _offset;
+      return operation.length! - _offset;
     }
     return double.infinity;
   }
@@ -651,8 +651,8 @@ class DeltaIterator {
       final opKey = op.key;
       final opAttributes = op.attributes;
       final _currentOffset = _offset;
-      final actualLength = math.min(op.length - _currentOffset, length);
+      final actualLength = math.min(op.length! - _currentOffset, length);
-      if (actualLength == op.length - _currentOffset) {
+      if (actualLength == op.length! - _currentOffset) {
         _index++;
         _offset = 0;
       } else {
@@ -660,12 +660,12 @@ class DeltaIterator {
       }
       final opData = op.isInsert && op.data is String
           ? (op.data as String)
-              .substring(_currentOffset, _currentOffset + actualLength)
+              .substring(_currentOffset as int, _currentOffset + (actualLength as int))
           : op.data;
       final opIsNotEmpty =
           opData is String ? opData.isNotEmpty : true; // embeds are never empty
       final opLength = opData is String ? opData.length : 1;
-      final int opActualLength = opIsNotEmpty ? opLength : actualLength;
+      final int opActualLength = opIsNotEmpty ? opLength : actualLength as int;
       return Operation._(opKey, opActualLength, opData, opAttributes);
     }
     return Operation.retain(length);
@@ -674,14 +674,14 @@ class DeltaIterator {
   /// Skips [length] characters in source delta.
   ///
   /// Returns last skipped operation, or `null` if there was nothing to skip.
-  Operation skip(int length) {
+  Operation? skip(int length) {
     var skipped = 0;
-    Operation op;
+    Operation? op;
     while (skipped < length && hasNext) {
       final opLength = peekLength();
       final skip = math.min(length - skipped, opLength);
-      op = next(skip);
+      op = next(skip as int);
-      skipped += op.length;
+      skipped += op.length!;
     }
     return op;
   }

lib/models/rules/delete.dart

@@ -9,7 +9,7 @@ abstract class DeleteRule extends Rule {
   RuleType get type => RuleType.DELETE;
 
   @override
-  validateArgs(int len, Object data, Attribute attribute) {
+  validateArgs(int? len, Object? data, Attribute? attribute) {
     assert(len != null);
     assert(data == null);
     assert(attribute == null);
@@ -21,10 +21,10 @@ class CatchAllDeleteRule extends DeleteRule {
 
   @override
   Delta applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
     return Delta()
       ..retain(index)
-      ..delete(len);
+      ..delete(len!);
   }
 }
 
@@ -32,8 +32,8 @@ class PreserveLineStyleOnMergeRule extends DeleteRule {
   const PreserveLineStyleOnMergeRule();
 
   @override
-  Delta applyRule(Delta document, int index,
+  Delta? applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
     DeltaIterator itr = DeltaIterator(document);
     itr.skip(index);
     Operation op = itr.next(1);
@@ -42,30 +42,30 @@ class PreserveLineStyleOnMergeRule extends DeleteRule {
     }
 
     bool isNotPlain = op.isNotPlain;
-    Map<String, dynamic> attrs = op.attributes;
+    Map<String, dynamic>? attrs = op.attributes;
 
-    itr.skip(len - 1);
+    itr.skip(len! - 1);
     Delta delta = Delta()
       ..retain(index)
       ..delete(len);
 
     while (itr.hasNext) {
       op = itr.next();
-      String text = op.data is String ? op.data as String : '';
+      String text = op.data is String ? (op.data as String?)! : '';
       int lineBreak = text.indexOf('\n');
       if (lineBreak == -1) {
-        delta..retain(op.length);
+        delta..retain(op.length!);
         continue;
       }
 
-      Map<String, dynamic> attributes = op.attributes == null
+      Map<String, dynamic>? attributes = op.attributes == null
           ? null
-          : op.attributes.map<String, dynamic>((String key, dynamic value) =>
+          : op.attributes!.map<String, dynamic>((String key, dynamic value) =>
               MapEntry<String, dynamic>(key, null));
 
       if (isNotPlain) {
         attributes ??= <String, dynamic>{};
-        attributes.addAll(attrs);
+        attributes.addAll(attrs!);
       }
       delta..retain(lineBreak)..retain(1, attributes);
       break;
@@ -78,17 +78,18 @@ class EnsureEmbedLineRule extends DeleteRule {
   const EnsureEmbedLineRule();
 
   @override
-  Delta applyRule(Delta document, int index,
+  Delta? applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
     DeltaIterator itr = DeltaIterator(document);
 
-    Operation op = itr.skip(index);
+    Operation? op = itr.skip(index);
-    int indexDelta = 0, lengthDelta = 0, remain = len;
+    int? indexDelta = 0, lengthDelta = 0, remain = len;
     bool embedFound = op != null && op.data is! String;
     bool hasLineBreakBefore =
-        !embedFound && (op == null || (op?.data as String).endsWith('\n'));
+        !embedFound && (op == null || (op.data as String).endsWith('\n'));
     if (embedFound) {
       Operation candidate = itr.next(1);
+      if (remain != null) {
         remain--;
         if (candidate.data == '\n') {
           indexDelta++;
@@ -101,10 +102,11 @@ class EnsureEmbedLineRule extends DeleteRule {
           }
         }
       }
+    }
 
-    op = itr.skip(remain);
+    op = itr.skip(remain!);
     if (op != null &&
-        (op?.data is String ? op.data as String : '').endsWith('\n')) {
+        (op.data is String ? op.data as String? : '')!.endsWith('\n')) {
       Operation candidate = itr.next(1);
       if (candidate.data is! String && !hasLineBreakBefore) {
         embedFound = true;
@@ -118,6 +120,6 @@ class EnsureEmbedLineRule extends DeleteRule {
 
     return Delta()
       ..retain(index + indexDelta)
-      ..delete(len + lengthDelta);
+      ..delete(len! + lengthDelta);
   }
 }

lib/models/rules/format.dart

@@ -9,7 +9,7 @@ abstract class FormatRule extends Rule {
   RuleType get type => RuleType.FORMAT;
 
   @override
-  validateArgs(int len, Object data, Attribute attribute) {
+  validateArgs(int? len, Object? data, Attribute? attribute) {
     assert(len != null);
     assert(data == null);
     assert(attribute != null);
@@ -20,9 +20,9 @@ class ResolveLineFormatRule extends FormatRule {
   const ResolveLineFormatRule();
 
   @override
-  Delta applyRule(Delta document, int index,
+  Delta? applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
-    if (attribute.scope != AttributeScope.BLOCK) {
+    if (attribute!.scope != AttributeScope.BLOCK) {
       return null;
     }
 
@@ -30,13 +30,13 @@ class ResolveLineFormatRule extends FormatRule {
     DeltaIterator itr = DeltaIterator(document);
     itr.skip(index);
     Operation op;
-    for (int cur = 0; cur < len && itr.hasNext; cur += op.length) {
+    for (int cur = 0; cur < len! && itr.hasNext; cur += op.length!) {
       op = itr.next(len - cur);
       if (op.data is! String || !(op.data as String).contains('\n')) {
-        delta.retain(op.length);
+        delta.retain(op.length!);
         continue;
       }
-      String text = op.data;
+      String text = op.data as String;
       Delta tmp = Delta();
       int offset = 0;
 
@@ -52,10 +52,10 @@ class ResolveLineFormatRule extends FormatRule {
 
     while (itr.hasNext) {
       op = itr.next();
-      String text = op.data is String ? op.data as String : '';
+      String text = op.data is String ? (op.data as String?)! : '';
       int lineBreak = text.indexOf('\n');
       if (lineBreak < 0) {
-        delta..retain(op.length);
+        delta..retain(op.length!);
         continue;
       }
       delta..retain(lineBreak)..retain(1, attribute.toJson());
@@ -69,28 +69,28 @@ class FormatLinkAtCaretPositionRule extends FormatRule {
   const FormatLinkAtCaretPositionRule();
 
   @override
-  Delta applyRule(Delta document, int index,
+  Delta? applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
-    if (attribute.key != Attribute.link.key || len > 0) {
+    if (attribute!.key != Attribute.link.key || len! > 0) {
       return null;
     }
 
     Delta delta = Delta();
     DeltaIterator itr = DeltaIterator(document);
-    Operation before = itr.skip(index), after = itr.next();
+    Operation? before = itr.skip(index), after = itr.next();
-    int beg = index, retain = 0;
+    int? beg = index, retain = 0;
     if (before != null && before.hasAttribute(attribute.key)) {
-      beg -= before.length;
+      beg -= before.length!;
       retain = before.length;
     }
-    if (after != null && after.hasAttribute(attribute.key)) {
+    if (after.hasAttribute(attribute.key)) {
-      retain += after.length;
+      if (retain != null) retain += after.length!;
     }
     if (retain == 0) {
       return null;
     }
 
-    delta..retain(beg)..retain(retain, attribute.toJson());
+    delta..retain(beg)..retain(retain!, attribute.toJson());
     return delta;
   }
 }
@@ -99,9 +99,9 @@ class ResolveInlineFormatRule extends FormatRule {
   const ResolveInlineFormatRule();
 
   @override
-  Delta applyRule(Delta document, int index,
+  Delta? applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
-    if (attribute.scope != AttributeScope.INLINE) {
+    if (attribute!.scope != AttributeScope.INLINE) {
       return null;
     }
 
@@ -110,12 +110,12 @@ class ResolveInlineFormatRule extends FormatRule {
     itr.skip(index);
 
     Operation op;
-    for (int cur = 0; cur < len && itr.hasNext; cur += op.length) {
+    for (int cur = 0; cur < len! && itr.hasNext; cur += op.length!) {
       op = itr.next(len - cur);
-      String text = op.data is String ? op.data as String : '';
+      String text = op.data is String ? (op.data as String?)! : '';
       int lineBreak = text.indexOf('\n');
       if (lineBreak < 0) {
-        delta.retain(op.length, attribute.toJson());
+        delta.retain(op.length!, attribute.toJson());
         continue;
       }
       int pos = 0;
@@ -124,8 +124,8 @@ class ResolveInlineFormatRule extends FormatRule {
         pos = lineBreak + 1;
         lineBreak = text.indexOf('\n', pos);
       }
-      if (pos < op.length) {
+      if (pos < op.length!) {
-        delta.retain(op.length - pos, attribute.toJson());
+        delta.retain(op.length! - pos, attribute.toJson());
       }
     }
 

lib/models/rules/insert.dart

@@ -11,7 +11,7 @@ abstract class InsertRule extends Rule {
   RuleType get type => RuleType.INSERT;
 
   @override
-  validateArgs(int len, Object data, Attribute attribute) {
+  validateArgs(int? len, Object? data, Attribute? attribute) {
     assert(len == null);
     assert(data != null);
     assert(attribute == null);
@@ -22,23 +22,21 @@ class PreserveLineStyleOnSplitRule extends InsertRule {
   const PreserveLineStyleOnSplitRule();
 
   @override
-  Delta applyRule(Delta document, int index,
+  Delta? applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
-    if (data is! String || (data as String) != '\n') {
+    if (data is! String || data != '\n') {
       return null;
     }
 
     DeltaIterator itr = DeltaIterator(document);
-    Operation before = itr.skip(index);
+    Operation? before = itr.skip(index);
     if (before == null ||
         before.data is! String ||
         (before.data as String).endsWith('\n')) {
       return null;
     }
     Operation after = itr.next();
-    if (after == null ||
+    if (after.data is! String || (after.data as String).startsWith('\n')) {
-        after.data is! String ||
-        (after.data as String).startsWith('\n')) {
       return null;
     }
 
@@ -50,8 +48,8 @@ class PreserveLineStyleOnSplitRule extends InsertRule {
       delta..insert('\n');
       return delta;
     }
-    Tuple2<Operation, int> nextNewLine = _getNextNewLine(itr);
+    Tuple2<Operation?, int?> nextNewLine = _getNextNewLine(itr);
-    Map<String, dynamic> attributes = nextNewLine?.item1?.attributes;
+    Map<String, dynamic>? attributes = nextNewLine.item1?.attributes;
 
     return delta..insert('\n', attributes);
   }
@@ -61,33 +59,33 @@ class PreserveBlockStyleOnInsertRule extends InsertRule {
   const PreserveBlockStyleOnInsertRule();
 
   @override
-  Delta applyRule(Delta document, int index,
+  Delta? applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
-    if (data is! String || !(data as String).contains('\n')) {
+    if (data is! String || !data.contains('\n')) {
       return null;
     }
 
     DeltaIterator itr = DeltaIterator(document);
     itr.skip(index);
 
-    Tuple2<Operation, int> nextNewLine = _getNextNewLine(itr);
+    Tuple2<Operation?, int?> nextNewLine = _getNextNewLine(itr);
     Style lineStyle =
         Style.fromJson(nextNewLine.item1?.attributes ?? <String, dynamic>{});
 
-    Attribute attribute = lineStyle.getBlockExceptHeader();
+    Attribute? attribute = lineStyle.getBlockExceptHeader();
     if (attribute == null) {
       return null;
     }
 
     var blockStyle = <String, dynamic>{attribute.key: attribute.value};
 
-    Map<String, dynamic> resetStyle;
+    Map<String, dynamic>? resetStyle;
 
     if (lineStyle.containsKey(Attribute.header.key)) {
       resetStyle = Attribute.header.toJson();
     }
 
-    List<String> lines = (data as String).split('\n');
+    List<String> lines = data.split('\n');
     Delta delta = Delta()..retain(index);
     for (int i = 0; i < lines.length; i++) {
       String line = lines[i];
@@ -102,9 +100,9 @@ class PreserveBlockStyleOnInsertRule extends InsertRule {
     }
 
     if (resetStyle != null) {
-      delta.retain(nextNewLine.item2);
+      delta.retain(nextNewLine.item2!);
       delta
-        ..retain((nextNewLine.item1.data as String).indexOf('\n'))
+        ..retain((nextNewLine.item1!.data as String).indexOf('\n'))
         ..retain(1, resetStyle);
     }
 
@@ -115,26 +113,26 @@ class PreserveBlockStyleOnInsertRule extends InsertRule {
 class AutoExitBlockRule extends InsertRule {
   const AutoExitBlockRule();
 
-  bool _isEmptyLine(Operation before, Operation after) {
+  bool _isEmptyLine(Operation? before, Operation? after) {
     if (before == null) {
       return true;
     }
     return before.data is String &&
         (before.data as String).endsWith('\n') &&
-        after.data is String &&
+        after!.data is String &&
         (after.data as String).startsWith('\n');
   }
 
   @override
-  Delta applyRule(Delta document, int index,
+  Delta? applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
-    if (data is! String || (data as String) != '\n') {
+    if (data is! String || data != '\n') {
       return null;
     }
 
     DeltaIterator itr = DeltaIterator(document);
-    Operation prev = itr.skip(index), cur = itr.next();
+    Operation? prev = itr.skip(index), cur = itr.next();
-    Attribute blockStyle =
+    Attribute? blockStyle =
         Style.fromJson(cur.attributes).getBlockExceptHeader();
     if (cur.isPlain || blockStyle == null) {
       return null;
@@ -147,10 +145,10 @@ class AutoExitBlockRule extends InsertRule {
       return null;
     }
 
-    Tuple2<Operation, int> nextNewLine = _getNextNewLine(itr);
+    Tuple2<Operation?, int?> nextNewLine = _getNextNewLine(itr);
     if (nextNewLine.item1 != null &&
-        nextNewLine.item1.attributes != null &&
+        nextNewLine.item1!.attributes != null &&
-        Style.fromJson(nextNewLine.item1.attributes).getBlockExceptHeader() ==
+        Style.fromJson(nextNewLine.item1!.attributes).getBlockExceptHeader() ==
             blockStyle) {
       return null;
     }
@@ -168,9 +166,9 @@ class ResetLineFormatOnNewLineRule extends InsertRule {
   const ResetLineFormatOnNewLineRule();
 
   @override
-  Delta applyRule(Delta document, int index,
+  Delta? applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
-    if (data is! String || (data as String) != '\n') {
+    if (data is! String || data != '\n') {
       return null;
     }
 
@@ -181,9 +179,9 @@ class ResetLineFormatOnNewLineRule extends InsertRule {
       return null;
     }
 
-    Map<String, dynamic> resetStyle;
+    Map<String, dynamic>? resetStyle;
     if (cur.attributes != null &&
-        cur.attributes.containsKey(Attribute.header.key)) {
+        cur.attributes!.containsKey(Attribute.header.key)) {
       resetStyle = Attribute.header.toJson();
     }
     return Delta()
@@ -198,33 +196,33 @@ class InsertEmbedsRule extends InsertRule {
   const InsertEmbedsRule();
 
   @override
-  Delta applyRule(Delta document, int index,
+  Delta? applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
     if (data is String) {
       return null;
     }
 
     Delta delta = Delta()..retain(index);
     DeltaIterator itr = DeltaIterator(document);
-    Operation prev = itr.skip(index), cur = itr.next();
+    Operation? prev = itr.skip(index), cur = itr.next();
 
-    String textBefore = prev?.data is String ? prev.data as String : '';
+    String? textBefore = prev?.data is String ? prev!.data as String? : '';
-    String textAfter = cur.data is String ? cur.data as String : '';
+    String textAfter = cur.data is String ? (cur.data as String?)! : '';
 
-    final isNewlineBefore = prev == null || textBefore.endsWith('\n');
+    final isNewlineBefore = prev == null || textBefore!.endsWith('\n');
     final isNewlineAfter = textAfter.startsWith('\n');
 
     if (isNewlineBefore && isNewlineAfter) {
       return delta..insert(data);
     }
 
-    Map<String, dynamic> lineStyle;
+    Map<String, dynamic>? lineStyle;
     if (textAfter.contains('\n')) {
       lineStyle = cur.attributes;
     } else {
       while (itr.hasNext) {
         Operation op = itr.next();
-        if ((op.data is String ? op.data as String : '').indexOf('\n') >= 0) {
+        if ((op.data is String ? op.data as String? : '')!.indexOf('\n') >= 0) {
           lineStyle = op.attributes;
           break;
         }
@@ -246,13 +244,13 @@ class ForceNewlineForInsertsAroundEmbedRule extends InsertRule {
   const ForceNewlineForInsertsAroundEmbedRule();
 
   @override
-  Delta applyRule(Delta document, int index,
+  Delta? applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
     if (data is! String) {
       return null;
     }
 
-    String text = data as String;
+    String text = data;
     DeltaIterator itr = DeltaIterator(document);
     final prev = itr.skip(index);
     final cur = itr.next();
@@ -277,14 +275,14 @@ class AutoFormatLinksRule extends InsertRule {
   const AutoFormatLinksRule();
 
   @override
-  Delta applyRule(Delta document, int index,
+  Delta? applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
-    if (data is! String || (data as String) != ' ') {
+    if (data is! String || data != ' ') {
       return null;
     }
 
     DeltaIterator itr = DeltaIterator(document);
-    Operation prev = itr.skip(index);
+    Operation? prev = itr.skip(index);
     if (prev == null || prev.data is! String) {
       return null;
     }
@@ -305,7 +303,7 @@ class AutoFormatLinksRule extends InsertRule {
       return Delta()
         ..retain(index - cand.length)
         ..retain(cand.length, attributes)
-        ..insert(data as String, prev.attributes);
+        ..insert(data, prev.attributes);
     } on FormatException {
       return null;
     }
@@ -316,22 +314,22 @@ class PreserveInlineStylesRule extends InsertRule {
   const PreserveInlineStylesRule();
 
   @override
-  Delta applyRule(Delta document, int index,
+  Delta? applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
-    if (data is! String || (data as String).contains('\n')) {
+    if (data is! String || data.contains('\n')) {
       return null;
     }
 
     DeltaIterator itr = DeltaIterator(document);
-    Operation prev = itr.skip(index);
+    Operation? prev = itr.skip(index);
     if (prev == null ||
         prev.data is! String ||
         (prev.data as String).contains('\n')) {
       return null;
     }
 
-    Map<String, dynamic> attributes = prev.attributes;
+    Map<String, dynamic>? attributes = prev.attributes;
-    String text = data as String;
+    String text = data;
     if (attributes == null || !attributes.containsKey(Attribute.link.key)) {
       return Delta()
         ..retain(index)
@@ -365,18 +363,19 @@ class CatchAllInsertRule extends InsertRule {
 
   @override
   Delta applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
     return Delta()
       ..retain(index)
       ..insert(data);
   }
 }
 
-Tuple2<Operation, int> _getNextNewLine(DeltaIterator iterator) {
+Tuple2<Operation?, int?> _getNextNewLine(DeltaIterator iterator) {
   Operation op;
-  for (int skipped = 0; iterator.hasNext; skipped += op.length) {
+  for (int skipped = 0; iterator.hasNext; skipped += op.length!) {
     op = iterator.next();
-    int lineBreak = (op.data is String ? op.data as String : '').indexOf('\n');
+    int lineBreak =
+        (op.data is String ? op.data as String? : '')!.indexOf('\n');
     if (lineBreak >= 0) {
       return Tuple2(op, skipped);
     }

lib/models/rules/rule.dart

@@ -11,8 +11,8 @@ enum RuleType { INSERT, DELETE, FORMAT }
 abstract class Rule {
   const Rule();
 
-  Delta apply(Delta document, int index,
+  Delta? apply(Delta document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
     assert(document != null);
     assert(index != null);
     validateArgs(len, data, attribute);
@@ -20,10 +20,10 @@ abstract class Rule {
         len: len, data: data, attribute: attribute);
   }
 
-  validateArgs(int len, Object data, Attribute attribute);
+  validateArgs(int? len, Object? data, Attribute? attribute);
 
-  Delta applyRule(Delta document, int index,
+  Delta? applyRule(Delta document, int index,
-      {int len, Object data, Attribute attribute});
+      {int? len, Object? data, Attribute? attribute});
 
   RuleType get type;
 }
@@ -53,7 +53,7 @@ class Rules {
   static Rules getInstance() => _instance;
 
   Delta apply(RuleType ruleType, Document document, int index,
-      {int len, Object data, Attribute attribute}) {
+      {int? len, Object? data, Attribute? attribute}) {
     final delta = document.toDelta();
     for (var rule in _rules) {
       if (rule.type != ruleType) {

lib/utils/color.dart

@@ -2,7 +2,7 @@ import 'dart:ui';
 
 import 'package:flutter/material.dart';
 
-Color stringToColor(String s) {
+Color stringToColor(String? s) {
   switch (s) {
     case 'transparent':
       return Colors.transparent;
@@ -106,7 +106,7 @@ Color stringToColor(String s) {
       return Colors.brown;
   }
 
-  if (s.startsWith('rgba')) {
+  if (s!.startsWith('rgba')) {
     s = s.substring(5); // trim left 'rgba('
     s = s.substring(0, s.length - 1); // trim right ')'
     final arr = s.split(',').map((e) => e.trim()).toList();

lib/utils/diff_delta.dart

@@ -76,7 +76,7 @@ int getPositionDelta(Delta user, Delta actual) {
   int diff = 0;
   while (userItr.hasNext || actualItr.hasNext) {
     final length = math.min(userItr.peekLength(), actualItr.peekLength());
-    Operation userOperation = userItr.next(length);
+    Operation userOperation = userItr.next(length as int);
     Operation actualOperation = actualItr.next(length);
     if (userOperation.length != actualOperation.length) {
       throw ('userOp ' +
@@ -88,18 +88,18 @@ int getPositionDelta(Delta user, Delta actual) {
     if (userOperation.key == actualOperation.key) {
       continue;
     } else if (userOperation.isInsert && actualOperation.isRetain) {
-      diff -= userOperation.length;
+      diff -= userOperation.length!;
     } else if (userOperation.isDelete && actualOperation.isRetain) {
-      diff += userOperation.length;
+      diff += userOperation.length!;
     } else if (userOperation.isRetain && actualOperation.isInsert) {
-      String operationTxt = '';
+      String? operationTxt = '';
       if (actualOperation.data is String) {
-        operationTxt = actualOperation.data as String;
+        operationTxt = actualOperation.data as String?;
       }
-      if (operationTxt.startsWith('\n')) {
+      if (operationTxt!.startsWith('\n')) {
         continue;
       }
-      diff += actualOperation.length;
+      diff += actualOperation.length!;
     }
   }
   return diff;

lib/widgets/box.dart

@@ -4,11 +4,11 @@ import 'package:flutter_quill/models/documents/nodes/container.dart';
 abstract class RenderContentProxyBox implements RenderBox {
   double getPreferredLineHeight();
 
-  Offset getOffsetForCaret(TextPosition position, Rect caretPrototype);
+  Offset getOffsetForCaret(TextPosition position, Rect? caretPrototype);
 
   TextPosition getPositionForOffset(Offset offset);
 
-  double getFullHeightForCaret(TextPosition position);
+  double? getFullHeightForCaret(TextPosition position);
 
   TextRange getWordBoundary(TextPosition position);
 
@@ -24,9 +24,9 @@ abstract class RenderEditableBox extends RenderBox {
 
   TextPosition getPositionForOffset(Offset offset);
 
-  TextPosition getPositionAbove(TextPosition position);
+  TextPosition? getPositionAbove(TextPosition position);
 
-  TextPosition getPositionBelow(TextPosition position);
+  TextPosition? getPositionBelow(TextPosition position);
 
   TextRange getWordBoundary(TextPosition position);
 

lib/widgets/controller.dart

@@ -14,7 +14,7 @@ class QuillController extends ChangeNotifier {
   TextSelection selection;
   Style toggledStyle = Style();
 
-  QuillController({@required this.document, @required this.selection})
+  QuillController({required this.document, required this.selection})
       : assert(document != null),
         assert(selection != null);
 
@@ -49,14 +49,14 @@ class QuillController extends ChangeNotifier {
     }
   }
 
-  void _handleHistoryChange(int len) {
+  void _handleHistoryChange(int? len) {
     if (len != 0) {
       // if (this.selection.extentOffset >= document.length) {
       // // cursor exceeds the length of document, position it in the end
       // updateSelection(
       //     TextSelection.collapsed(offset: document.length), ChangeSource.LOCAL);
       updateSelection(
-          TextSelection.collapsed(offset: this.selection.baseOffset + len),
+          TextSelection.collapsed(offset: this.selection.baseOffset + len!),
           ChangeSource.LOCAL);
     } else {
       // no need to move cursor
@@ -75,11 +75,11 @@ class QuillController extends ChangeNotifier {
 
   get hasRedo => document.hasRedo;
 
-  replaceText(int index, int len, Object data, TextSelection textSelection) {
+  replaceText(int index, int len, Object? data, TextSelection? textSelection) {
     assert(data is String || data is Embeddable);
 
-    Delta delta;
+    Delta? delta;
-    if (len > 0 || data is! String || (data as String).isNotEmpty) {
+    if (len > 0 || data is! String || data.isNotEmpty) {
       try {
         delta = document.replace(index, len, data);
       } catch (e) {
@@ -137,8 +137,8 @@ class QuillController extends ChangeNotifier {
     notifyListeners();
   }
 
-  formatText(int index, int len, Attribute attribute) {
+  formatText(int index, int len, Attribute? attribute) {
-    if (len == 0 && attribute.isInline && attribute.key != Attribute.link.key) {
+    if (len == 0 && attribute!.isInline && attribute.key != Attribute.link.key) {
       toggledStyle = toggledStyle.put(attribute);
     }
 
@@ -152,7 +152,7 @@ class QuillController extends ChangeNotifier {
     notifyListeners();
   }
 
-  formatSelection(Attribute attribute) {
+  formatSelection(Attribute? attribute) {
     formatText(selection.start, selection.end - selection.start, attribute);
   }
 

lib/widgets/cursor.dart

@@ -11,25 +11,22 @@ class CursorStyle {
   final Color color;
   final Color backgroundColor;
   final double width;
-  final double height;
+  final double? height;
-  final Radius radius;
+  final Radius? radius;
-  final Offset offset;
+  final Offset? offset;
   final bool opacityAnimates;
   final bool paintAboveText;
 
   const CursorStyle({
-    @required this.color,
+    required this.color,
-    @required this.backgroundColor,
+    required this.backgroundColor,
     this.width = 1.0,
     this.height,
     this.radius,
     this.offset,
     this.opacityAnimates = false,
     this.paintAboveText = false,
-  })  : assert(color != null),
+  });
-        assert(backgroundColor != null),
-        assert(opacityAnimates != null),
-        assert(paintAboveText != null);
 
   @override
   bool operator ==(Object other) =>
@@ -61,19 +58,17 @@ class CursorCont extends ChangeNotifier {
   final ValueNotifier<bool> show;
   final ValueNotifier<bool> _blink;
   final ValueNotifier<Color> color;
-  AnimationController _blinkOpacityCont;
+  late AnimationController _blinkOpacityCont;
-  Timer _cursorTimer;
+  Timer? _cursorTimer;
   bool _targetCursorVisibility = false;
   CursorStyle _style;
 
   CursorCont({
-    @required ValueNotifier<bool> show,
+    required ValueNotifier<bool> show,
-    @required CursorStyle style,
+    required CursorStyle style,
-    @required TickerProvider tickerProvider,
+    required TickerProvider tickerProvider,
-  })  : assert(show != null),
+  })  : 
-        assert(style != null),
+        show = show,
-        assert(tickerProvider != null),
-        show = show ?? ValueNotifier<bool>(false),
         _style = style,
         _blink = ValueNotifier(false),
         color = ValueNotifier(style.color) {
@@ -89,7 +84,6 @@ class CursorCont extends ChangeNotifier {
   CursorStyle get style => _style;
 
   set style(CursorStyle value) {
-    assert(value != null);
     if (_style == value) return;
     _style = value;
     notifyListeners();
@@ -161,9 +155,9 @@ class CursorCont extends ChangeNotifier {
 }
 
 class CursorPainter {
-  final RenderContentProxyBox editable;
+  final RenderContentProxyBox? editable;
   final CursorStyle style;
-  final Rect prototype;
+  final Rect? prototype;
   final Color color;
   final double devicePixelRatio;
 
@@ -174,17 +168,17 @@ class CursorPainter {
     assert(prototype != null);
 
     Offset caretOffset =
-        editable.getOffsetForCaret(position, prototype) + offset;
+        editable!.getOffsetForCaret(position, prototype) + offset;
-    Rect caretRect = prototype.shift(caretOffset);
+    Rect caretRect = prototype!.shift(caretOffset);
     if (style.offset != null) {
-      caretRect = caretRect.shift(style.offset);
+      caretRect = caretRect.shift(style.offset!);
     }
 
     if (caretRect.left < 0.0) {
       caretRect = caretRect.shift(Offset(-caretRect.left, 0.0));
     }
 
-    double caretHeight = editable.getFullHeightForCaret(position);
+    double? caretHeight = editable!.getFullHeightForCaret(position);
     if (caretHeight != null) {
       switch (defaultTargetPlatform) {
         case TargetPlatform.android:
@@ -212,7 +206,7 @@ class CursorPainter {
       }
     }
 
-    Offset caretPosition = editable.localToGlobal(caretRect.topLeft);
+    Offset caretPosition = editable!.localToGlobal(caretRect.topLeft);
     double pixelMultiple = 1.0 / devicePixelRatio;
     caretRect = caretRect.shift(Offset(
         caretPosition.dx.isFinite
@@ -230,7 +224,7 @@ class CursorPainter {
       return;
     }
 
-    RRect caretRRect = RRect.fromRectAndRadius(caretRect, style.radius);
+    RRect caretRRect = RRect.fromRectAndRadius(caretRect, style.radius!);
     canvas.drawRRect(caretRRect, paint);
   }
 }

lib/widgets/default_styles.dart

@@ -6,9 +6,9 @@ class QuillStyles extends InheritedWidget {
   final DefaultStyles data;
 
   QuillStyles({
-    Key key,
+    Key? key,
-    @required this.data,
+    required this.data,
-    @required Widget child,
+    required Widget child,
   })  : assert(data != null),
         assert(child != null),
         super(key: key, child: child);
@@ -18,13 +18,13 @@ class QuillStyles extends InheritedWidget {
     return data != oldWidget.data;
   }
 
-  static DefaultStyles getStyles(BuildContext context, bool nullOk) {
+  static DefaultStyles? getStyles(BuildContext context, bool nullOk) {
     var widget = context.dependOnInheritedWidgetOfExactType<QuillStyles>();
     if (widget == null && nullOk) {
       return null;
     }
     assert(widget != null);
-    return widget.data;
+    return widget!.data;
   }
 }
 
@@ -35,31 +35,31 @@ class DefaultTextBlockStyle {
 
   final Tuple2<double, double> lineSpacing;
 
-  final BoxDecoration decoration;
+  final BoxDecoration? decoration;
 
   DefaultTextBlockStyle(
       this.style, this.verticalSpacing, this.lineSpacing, this.decoration);
 }
 
 class DefaultStyles {
-  final DefaultTextBlockStyle h1;
+  final DefaultTextBlockStyle? h1;
-  final DefaultTextBlockStyle h2;
+  final DefaultTextBlockStyle? h2;
-  final DefaultTextBlockStyle h3;
+  final DefaultTextBlockStyle? h3;
-  final DefaultTextBlockStyle paragraph;
+  final DefaultTextBlockStyle? paragraph;
-  final TextStyle bold;
+  final TextStyle? bold;
-  final TextStyle italic;
+  final TextStyle? italic;
-  final TextStyle underline;
+  final TextStyle? underline;
-  final TextStyle strikeThrough;
+  final TextStyle? strikeThrough;
-  final TextStyle sizeSmall; // 'small'
+  final TextStyle? sizeSmall; // 'small'
-  final TextStyle sizeLarge; // 'large'
+  final TextStyle? sizeLarge; // 'large'
-  final TextStyle sizeHuge; // 'huge'
+  final TextStyle? sizeHuge; // 'huge'
-  final TextStyle link;
+  final TextStyle? link;
-  final DefaultTextBlockStyle placeHolder;
+  final DefaultTextBlockStyle? placeHolder;
-  final DefaultTextBlockStyle lists;
+  final DefaultTextBlockStyle? lists;
-  final DefaultTextBlockStyle quote;
+  final DefaultTextBlockStyle? quote;
-  final DefaultTextBlockStyle code;
+  final DefaultTextBlockStyle? code;
-  final DefaultTextBlockStyle indent;
+  final DefaultTextBlockStyle? indent;
-  final DefaultTextBlockStyle align;
+  final DefaultTextBlockStyle? align;
 
   DefaultStyles(
       {this.h1,
@@ -109,7 +109,7 @@ class DefaultStyles {
         h1: DefaultTextBlockStyle(
             defaultTextStyle.style.copyWith(
               fontSize: 34.0,
-              color: defaultTextStyle.style.color.withOpacity(0.70),
+              color: defaultTextStyle.style.color!.withOpacity(0.70),
               height: 1.15,
               fontWeight: FontWeight.w300,
             ),
@@ -119,7 +119,7 @@ class DefaultStyles {
         h2: DefaultTextBlockStyle(
             defaultTextStyle.style.copyWith(
               fontSize: 24.0,
-              color: defaultTextStyle.style.color.withOpacity(0.70),
+              color: defaultTextStyle.style.color!.withOpacity(0.70),
               height: 1.15,
               fontWeight: FontWeight.normal,
             ),
@@ -129,7 +129,7 @@ class DefaultStyles {
         h3: DefaultTextBlockStyle(
             defaultTextStyle.style.copyWith(
               fontSize: 20.0,
-              color: defaultTextStyle.style.color.withOpacity(0.70),
+              color: defaultTextStyle.style.color!.withOpacity(0.70),
               height: 1.25,
               fontWeight: FontWeight.w500,
             ),
@@ -158,7 +158,7 @@ class DefaultStyles {
         lists: DefaultTextBlockStyle(
             baseStyle, baseSpacing, Tuple2(0.0, 6.0), null),
         quote: DefaultTextBlockStyle(
-            TextStyle(color: baseStyle.color.withOpacity(0.6)),
+            TextStyle(color: baseStyle.color!.withOpacity(0.6)),
             baseSpacing,
             Tuple2(6.0, 2.0),
             BoxDecoration(

lib/widgets/delegate.dart

@@ -14,7 +14,7 @@ abstract class EditorTextSelectionGestureDetectorBuilderDelegate {
 
   bool getForcePressEnabled();
 
-  bool getSelectionEnabled();
+  bool? getSelectionEnabled();
 }
 
 class EditorTextSelectionGestureDetectorBuilder {
@@ -24,18 +24,18 @@ class EditorTextSelectionGestureDetectorBuilder {
   EditorTextSelectionGestureDetectorBuilder(this.delegate)
       : assert(delegate != null);
 
-  EditorState getEditor() {
+  EditorState? getEditor() {
     return delegate.getEditableTextKey().currentState;
   }
 
-  RenderEditor getRenderEditor() {
+  RenderEditor? getRenderEditor() {
-    return this.getEditor().getRenderEditor();
+    return this.getEditor()!.getRenderEditor();
   }
 
   onTapDown(TapDownDetails details) {
-    getRenderEditor().handleTapDown(details);
+    getRenderEditor()!.handleTapDown(details);
 
-    PointerDeviceKind kind = details.kind;
+    PointerDeviceKind? kind = details.kind;
     shouldShowSelectionToolbar = kind == null ||
         kind == PointerDeviceKind.touch ||
         kind == PointerDeviceKind.stylus;
@@ -44,8 +44,8 @@ class EditorTextSelectionGestureDetectorBuilder {
   onForcePressStart(ForcePressDetails details) {
     assert(delegate.getForcePressEnabled());
     shouldShowSelectionToolbar = true;
-    if (delegate.getSelectionEnabled()) {
+    if (delegate.getSelectionEnabled()!) {
-      getRenderEditor().selectWordsInRange(
+      getRenderEditor()!.selectWordsInRange(
         details.globalPosition,
         null,
         SelectionChangedCause.forcePress,
@@ -55,27 +55,27 @@ class EditorTextSelectionGestureDetectorBuilder {
 
   onForcePressEnd(ForcePressDetails details) {
     assert(delegate.getForcePressEnabled());
-    getRenderEditor().selectWordsInRange(
+    getRenderEditor()!.selectWordsInRange(
       details.globalPosition,
       null,
       SelectionChangedCause.forcePress,
     );
     if (shouldShowSelectionToolbar) {
-      getEditor().showToolbar();
+      getEditor()!.showToolbar();
     }
   }
 
   onSingleTapUp(TapUpDetails details) {
-    if (delegate.getSelectionEnabled()) {
+    if (delegate.getSelectionEnabled()!) {
-      getRenderEditor().selectWordEdge(SelectionChangedCause.tap);
+      getRenderEditor()!.selectWordEdge(SelectionChangedCause.tap);
     }
   }
 
   onSingleTapCancel() {}
 
   onSingleLongTapStart(LongPressStartDetails details) {
-    if (delegate.getSelectionEnabled()) {
+    if (delegate.getSelectionEnabled()!) {
-      getRenderEditor().selectPositionAt(
+      getRenderEditor()!.selectPositionAt(
         details.globalPosition,
         null,
         SelectionChangedCause.longPress,
@@ -84,8 +84,8 @@ class EditorTextSelectionGestureDetectorBuilder {
   }
 
   onSingleLongTapMoveUpdate(LongPressMoveUpdateDetails details) {
-    if (delegate.getSelectionEnabled()) {
+    if (delegate.getSelectionEnabled()!) {
-      getRenderEditor().selectPositionAt(
+      getRenderEditor()!.selectPositionAt(
         details.globalPosition,
         null,
         SelectionChangedCause.longPress,
@@ -95,21 +95,21 @@ class EditorTextSelectionGestureDetectorBuilder {
 
   onSingleLongTapEnd(LongPressEndDetails details) {
     if (shouldShowSelectionToolbar) {
-      getEditor().showToolbar();
+      getEditor()!.showToolbar();
     }
   }
 
   onDoubleTapDown(TapDownDetails details) {
-    if (delegate.getSelectionEnabled()) {
+    if (delegate.getSelectionEnabled()!) {
-      getRenderEditor().selectWord(SelectionChangedCause.tap);
+      getRenderEditor()!.selectWord(SelectionChangedCause.tap);
       if (shouldShowSelectionToolbar) {
-        getEditor().showToolbar();
+        getEditor()!.showToolbar();
       }
     }
   }
 
   onDragSelectionStart(DragStartDetails details) {
-    getRenderEditor().selectPositionAt(
+    getRenderEditor()!.selectPositionAt(
       details.globalPosition,
       null,
       SelectionChangedCause.drag,
@@ -118,7 +118,7 @@ class EditorTextSelectionGestureDetectorBuilder {
 
   onDragSelectionUpdate(
       DragStartDetails startDetails, DragUpdateDetails updateDetails) {
-    getRenderEditor().selectPositionAt(
+    getRenderEditor()!.selectPositionAt(
       startDetails.globalPosition,
       updateDetails.globalPosition,
       SelectionChangedCause.drag,

lib/widgets/editor.dart

@@ -53,9 +53,9 @@ abstract class EditorState extends State<RawEditor> {
 
   void setTextEditingValue(TextEditingValue value);
 
-  RenderEditor getRenderEditor();
+  RenderEditor? getRenderEditor();
 
-  EditorTextSelectionOverlay getSelectionOverlay();
+  EditorTextSelectionOverlay? getSelectionOverlay();
 
   bool showToolbar();
 
@@ -146,35 +146,35 @@ class QuillEditor extends StatefulWidget {
   final bool scrollable;
   final EdgeInsetsGeometry padding;
   final bool autoFocus;
-  final bool showCursor;
+  final bool? showCursor;
   final bool readOnly;
-  final String placeholder;
+  final String? placeholder;
-  final bool enableInteractiveSelection;
+  final bool? enableInteractiveSelection;
-  final double minHeight;
+  final double? minHeight;
-  final double maxHeight;
+  final double? maxHeight;
-  final DefaultStyles customStyles;
+  final DefaultStyles? customStyles;
   final bool expands;
   final TextCapitalization textCapitalization;
   final Brightness keyboardAppearance;
-  final ScrollPhysics scrollPhysics;
+  final ScrollPhysics? scrollPhysics;
-  final ValueChanged<String> onLaunchUrl;
+  final ValueChanged<String>? onLaunchUrl;
   final EmbedBuilder embedBuilder;
 
   QuillEditor(
-      {@required this.controller,
+      {required this.controller,
-      @required this.focusNode,
+      required this.focusNode,
-      @required this.scrollController,
+      required this.scrollController,
-      @required this.scrollable,
+      required this.scrollable,
-      @required this.padding,
+      required this.padding,
-      @required this.autoFocus,
+      required this.autoFocus,
       this.showCursor,
-      @required this.readOnly,
+      required this.readOnly,
       this.placeholder,
       this.enableInteractiveSelection,
       this.minHeight,
       this.maxHeight,
       this.customStyles,
-      @required this.expands,
+      required this.expands,
       this.textCapitalization = TextCapitalization.sentences,
       this.keyboardAppearance = Brightness.light,
       this.scrollPhysics,
@@ -190,7 +190,7 @@ class QuillEditor extends StatefulWidget {
         assert(embedBuilder != null);
 
   factory QuillEditor.basic(
-      {@required QuillController controller, bool readOnly}) {
+      {required QuillController controller, required bool readOnly}) {
     return QuillEditor(
         controller: controller,
         scrollController: ScrollController(),
@@ -210,7 +210,7 @@ class QuillEditor extends StatefulWidget {
 class _QuillEditorState extends State<QuillEditor>
     implements EditorTextSelectionGestureDetectorBuilderDelegate {
   final GlobalKey<EditorState> _editorKey = GlobalKey<EditorState>();
-  EditorTextSelectionGestureDetectorBuilder _selectionGestureDetectorBuilder;
+  late EditorTextSelectionGestureDetectorBuilder _selectionGestureDetectorBuilder;
 
   @override
   void initState() {
@@ -227,10 +227,10 @@ class _QuillEditorState extends State<QuillEditor>
     TextSelectionControls textSelectionControls;
     bool paintCursorAboveText;
     bool cursorOpacityAnimates;
-    Offset cursorOffset;
+    Offset? cursorOffset;
-    Color cursorColor;
+    Color? cursorColor;
     Color selectionColor;
-    Radius cursorRadius;
+    Radius? cursorRadius;
 
     switch (theme.platform) {
       case TargetPlatform.android:
@@ -301,7 +301,7 @@ class _QuillEditorState extends State<QuillEditor>
           selectionColor,
           textSelectionControls,
           widget.keyboardAppearance,
-          widget.enableInteractiveSelection,
+          widget.enableInteractiveSelection!,
           widget.scrollPhysics,
           widget.embedBuilder),
     );
@@ -318,12 +318,12 @@ class _QuillEditorState extends State<QuillEditor>
   }
 
   @override
-  bool getSelectionEnabled() {
+  bool? getSelectionEnabled() {
     return widget.enableInteractiveSelection;
   }
 
   _requestKeyboard() {
-    _editorKey.currentState.requestKeyboard();
+    _editorKey.currentState!.requestKeyboard();
   }
 }
 
@@ -336,8 +336,8 @@ class _QuillEditorSelectionGestureDetectorBuilder
   @override
   onForcePressStart(ForcePressDetails details) {
     super.onForcePressStart(details);
-    if (delegate.getSelectionEnabled() && shouldShowSelectionToolbar) {
+    if (delegate.getSelectionEnabled()! && shouldShowSelectionToolbar) {
-      getEditor().showToolbar();
+      getEditor()!.showToolbar();
     }
   }
 
@@ -346,13 +346,13 @@ class _QuillEditorSelectionGestureDetectorBuilder
 
   @override
   void onSingleLongTapMoveUpdate(LongPressMoveUpdateDetails details) {
-    if (!delegate.getSelectionEnabled()) {
+    if (!delegate.getSelectionEnabled()!) {
       return;
     }
     switch (Theme.of(_state.context).platform) {
       case TargetPlatform.iOS:
       case TargetPlatform.macOS:
-        getRenderEditor().selectPositionAt(
+        getRenderEditor()!.selectPositionAt(
           details.globalPosition,
           null,
           SelectionChangedCause.longPress,
@@ -362,7 +362,7 @@ class _QuillEditorSelectionGestureDetectorBuilder
       case TargetPlatform.fuchsia:
       case TargetPlatform.linux:
       case TargetPlatform.windows:
-        getRenderEditor().selectWordsInRange(
+        getRenderEditor()!.selectWordsInRange(
           details.globalPosition - details.offsetFromOrigin,
           details.globalPosition,
           SelectionChangedCause.longPress,
@@ -378,9 +378,9 @@ class _QuillEditorSelectionGestureDetectorBuilder
       return false;
     }
     TextPosition pos =
-        getRenderEditor().getPositionForOffset(details.globalPosition);
+        getRenderEditor()!.getPositionForOffset(details.globalPosition);
     containerNode.ChildQuery result =
-        getEditor().widget.controller.document.queryChild(pos.offset);
+        getEditor()!.widget.controller.document.queryChild(pos.offset);
     if (result.node == null) {
       return false;
     }
@@ -391,7 +391,7 @@ class _QuillEditorSelectionGestureDetectorBuilder
       if (line.length == 1) {
         // tapping when no text yet on this line
         _flipListCheckbox(pos, line, segmentResult);
-        getEditor().widget.controller.updateSelection(
+        getEditor()!.widget.controller.updateSelection(
             TextSelection.collapsed(offset: pos.offset), ChangeSource.LOCAL);
         return true;
       }
@@ -399,33 +399,33 @@ class _QuillEditorSelectionGestureDetectorBuilder
     }
     leaf.Leaf segment = segmentResult.node as leaf.Leaf;
     if (segment.style.containsKey(Attribute.link.key)) {
-      var launchUrl = getEditor().widget.onLaunchUrl;
+      var launchUrl = getEditor()!.widget.onLaunchUrl;
       if (launchUrl == null) {
         launchUrl = _launchUrl;
       }
-      String link = segment.style.attributes[Attribute.link.key].value;
+      String? link = segment.style.attributes[Attribute.link.key]!.value;
-      if (getEditor().widget.readOnly && link != null) {
+      if (getEditor()!.widget.readOnly && link != null) {
         link = link.trim();
         if (!linkPrefixes
-            .any((linkPrefix) => link.toLowerCase().startsWith(linkPrefix))) {
+            .any((linkPrefix) => link!.toLowerCase().startsWith(linkPrefix))) {
           link = 'https://$link';
         }
         launchUrl(link);
       }
       return false;
     }
-    if (getEditor().widget.readOnly && segment.value is BlockEmbed) {
+    if (getEditor()!.widget.readOnly && segment.value is BlockEmbed) {
       BlockEmbed blockEmbed = segment.value as BlockEmbed;
       if (blockEmbed.type == 'image') {
         final String imageUrl = blockEmbed.data;
         Navigator.push(
-          getEditor().context,
+          getEditor()!.context,
           MaterialPageRoute(
             builder: (context) => ImageTapWrapper(
               imageProvider: imageUrl.startsWith('http')
                   ? NetworkImage(imageUrl)
                   : isBase64(imageUrl)
-                      ? Image.memory(base64.decode(imageUrl))
+                      ? Image.memory(base64.decode(imageUrl)) as ImageProvider<Object>?
                       : FileImage(io.File(imageUrl)),
             ),
           ),
@@ -441,25 +441,25 @@ class _QuillEditorSelectionGestureDetectorBuilder
 
   bool _flipListCheckbox(
       TextPosition pos, Line line, containerNode.ChildQuery segmentResult) {
-    if (getEditor().widget.readOnly ||
+    if (getEditor()!.widget.readOnly ||
         !line.style.containsKey(Attribute.list.key) ||
         segmentResult.offset != 0) {
       return false;
     }
     // segmentResult.offset == 0 means tap at the beginning of the TextLine
-    String listVal = line.style.attributes[Attribute.list.key].value;
+    String? listVal = line.style.attributes[Attribute.list.key]!.value;
     if (listVal == Attribute.unchecked.value) {
-      getEditor()
+      getEditor()!
           .widget
           .controller
           .formatText(pos.offset, 0, Attribute.checked);
     } else if (listVal == Attribute.checked.value) {
-      getEditor()
+      getEditor()!
           .widget
           .controller
           .formatText(pos.offset, 0, Attribute.unchecked);
     }
-    getEditor().widget.controller.updateSelection(
+    getEditor()!.widget.controller.updateSelection(
         TextSelection.collapsed(offset: pos.offset), ChangeSource.LOCAL);
     return true;
   }
@@ -470,11 +470,11 @@ class _QuillEditorSelectionGestureDetectorBuilder
 
   @override
   onSingleTapUp(TapUpDetails details) {
-    getEditor().hideToolbar();
+    getEditor()!.hideToolbar();
 
     bool positionSelected = _onTapping(details);
 
-    if (delegate.getSelectionEnabled() && !positionSelected) {
+    if (delegate.getSelectionEnabled()! && !positionSelected) {
       switch (Theme.of(_state.context).platform) {
         case TargetPlatform.iOS:
         case TargetPlatform.macOS:
@@ -482,11 +482,11 @@ class _QuillEditorSelectionGestureDetectorBuilder
             case PointerDeviceKind.mouse:
             case PointerDeviceKind.stylus:
             case PointerDeviceKind.invertedStylus:
-              getRenderEditor().selectPosition(SelectionChangedCause.tap);
+              getRenderEditor()!.selectPosition(SelectionChangedCause.tap);
               break;
             case PointerDeviceKind.touch:
             case PointerDeviceKind.unknown:
-              getRenderEditor().selectWordEdge(SelectionChangedCause.tap);
+              getRenderEditor()!.selectWordEdge(SelectionChangedCause.tap);
               break;
           }
           break;
@@ -494,7 +494,7 @@ class _QuillEditorSelectionGestureDetectorBuilder
         case TargetPlatform.fuchsia:
         case TargetPlatform.linux:
         case TargetPlatform.windows:
-          getRenderEditor().selectPosition(SelectionChangedCause.tap);
+          getRenderEditor()!.selectPosition(SelectionChangedCause.tap);
           break;
       }
     }
@@ -503,11 +503,11 @@ class _QuillEditorSelectionGestureDetectorBuilder
 
   @override
   void onSingleLongTapStart(LongPressStartDetails details) {
-    if (delegate.getSelectionEnabled()) {
+    if (delegate.getSelectionEnabled()!) {
       switch (Theme.of(_state.context).platform) {
         case TargetPlatform.iOS:
         case TargetPlatform.macOS:
-          getRenderEditor().selectPositionAt(
+          getRenderEditor()!.selectPositionAt(
             details.globalPosition,
             null,
             SelectionChangedCause.longPress,
@@ -517,7 +517,7 @@ class _QuillEditorSelectionGestureDetectorBuilder
         case TargetPlatform.fuchsia:
         case TargetPlatform.linux:
         case TargetPlatform.windows:
-          getRenderEditor().selectWord(SelectionChangedCause.longPress);
+          getRenderEditor()!.selectWord(SelectionChangedCause.longPress);
           Feedback.forLongPress(_state.context);
           break;
         default:
@@ -548,7 +548,7 @@ class RenderEditor extends RenderEditableContainerBox
   final ValueNotifier<bool> _selectionEndInViewport = ValueNotifier<bool>(true);
 
   RenderEditor(
-      List<RenderEditableBox> children,
+      List<RenderEditableBox>? children,
       TextDirection textDirection,
       EdgeInsetsGeometry padding,
       this.document,
@@ -622,7 +622,7 @@ class RenderEditor extends RenderEditableContainerBox
           offset:
               textSelection.extentOffset - child.getContainer().getOffset());
       Offset localOffset = child.getOffsetForCaret(localPosition);
-      BoxParentData parentData = child.parentData;
+      BoxParentData parentData = child.parentData as BoxParentData;
       return <TextSelectionPoint>[
         TextSelectionPoint(
             Offset(0.0, child.preferredLineHeight(localPosition)) +
@@ -632,7 +632,7 @@ class RenderEditor extends RenderEditableContainerBox
       ];
     }
 
-    Node baseNode = _container.queryChild(textSelection.start, false).node;
+    Node? baseNode = _container.queryChild(textSelection.start, false).node;
 
     var baseChild = firstChild;
     while (baseChild != null) {
@@ -643,7 +643,7 @@ class RenderEditor extends RenderEditableContainerBox
     }
     assert(baseChild != null);
 
-    BoxParentData baseParentData = baseChild.parentData;
+    BoxParentData baseParentData = baseChild!.parentData as BoxParentData;
     TextSelection baseSelection =
         localSelection(baseChild.getContainer(), textSelection, true);
     TextSelectionPoint basePoint =
@@ -651,8 +651,8 @@ class RenderEditor extends RenderEditableContainerBox
     basePoint = TextSelectionPoint(
         basePoint.point + baseParentData.offset, basePoint.direction);
 
-    Node extentNode = _container.queryChild(textSelection.end, false).node;
+    Node? extentNode = _container.queryChild(textSelection.end, false).node;
-    var extentChild = baseChild;
+    RenderEditableBox? extentChild = baseChild;
     while (extentChild != null) {
       if (extentChild.getContainer() == extentNode) {
         break;
@@ -661,7 +661,7 @@ class RenderEditor extends RenderEditableContainerBox
     }
     assert(extentChild != null);
 
-    BoxParentData extentParentData = extentChild.parentData;
+    BoxParentData extentParentData = extentChild!.parentData as BoxParentData;
     TextSelection extentSelection =
         localSelection(extentChild.getContainer(), textSelection, true);
     TextSelectionPoint extentPoint =
@@ -672,7 +672,7 @@ class RenderEditor extends RenderEditableContainerBox
     return <TextSelectionPoint>[basePoint, extentPoint];
   }
 
-  Offset _lastTapDownPosition;
+  Offset? _lastTapDownPosition;
 
   @override
   handleTapDown(TapDownDetails details) {
@@ -682,7 +682,7 @@ class RenderEditor extends RenderEditableContainerBox
   @override
   selectWordsInRange(
     Offset from,
-    Offset to,
+    Offset? to,
     SelectionChangedCause cause,
   ) {
     assert(cause != null);
@@ -729,7 +729,7 @@ class RenderEditor extends RenderEditableContainerBox
     if (onSelectionChanged == null) {
       return;
     }
-    TextPosition position = getPositionForOffset(_lastTapDownPosition);
+    TextPosition position = getPositionForOffset(_lastTapDownPosition!);
     RenderEditableBox child = childAtPosition(position);
     int nodeOffset = child.getContainer().getOffset();
     TextPosition localPosition = TextPosition(
@@ -759,7 +759,7 @@ class RenderEditor extends RenderEditableContainerBox
   @override
   selectPositionAt(
     Offset from,
-    Offset to,
+    Offset? to,
     SelectionChangedCause cause,
   ) {
     assert(cause != null);
@@ -768,7 +768,7 @@ class RenderEditor extends RenderEditableContainerBox
       return;
     }
     TextPosition fromPosition = getPositionForOffset(from);
-    TextPosition toPosition = to == null ? null : getPositionForOffset(to);
+    TextPosition? toPosition = to == null ? null : getPositionForOffset(to);
 
     int baseOffset = fromPosition.offset;
     int extentOffset = fromPosition.offset;
@@ -787,12 +787,12 @@ class RenderEditor extends RenderEditableContainerBox
 
   @override
   selectWord(SelectionChangedCause cause) {
-    selectWordsInRange(_lastTapDownPosition, null, cause);
+    selectWordsInRange(_lastTapDownPosition!, null, cause);
   }
 
   @override
   selectPosition(SelectionChangedCause cause) {
-    selectPositionAt(_lastTapDownPosition, null, cause);
+    selectPositionAt(_lastTapDownPosition!, null, cause);
   }
 
   @override
@@ -837,7 +837,7 @@ class RenderEditor extends RenderEditableContainerBox
   }
 
   @override
-  bool hitTestChildren(BoxHitTestResult result, {Offset position}) {
+  bool hitTestChildren(BoxHitTestResult result, {required Offset position}) {
     return defaultHitTestChildren(result, position: position);
   }
 
@@ -877,9 +877,9 @@ class RenderEditor extends RenderEditableContainerBox
   @override
   TextPosition getPositionForOffset(Offset offset) {
     Offset local = globalToLocal(offset);
-    RenderEditableBox child = childAtOffset(local);
+    RenderEditableBox child = childAtOffset(local)!;
 
-    BoxParentData parentData = child.parentData;
+    BoxParentData parentData = child.parentData as BoxParentData;
     Offset localOffset = local - parentData.offset;
     TextPosition localPosition = child.getPositionForOffset(localOffset);
     return TextPosition(
@@ -888,7 +888,7 @@ class RenderEditor extends RenderEditableContainerBox
     );
   }
 
-  double getOffsetToRevealCursor(
+  double? getOffsetToRevealCursor(
       double viewportHeight, double scrollOffset, double offsetInViewport) {
     List<TextSelectionPoint> endpoints = getEndpointsForSelection(selection);
     TextSelectionPoint endpoint = endpoints.first;
@@ -902,7 +902,7 @@ class RenderEditor extends RenderEditableContainerBox
         kMargin +
         offsetInViewport;
     final caretBottom = endpoint.point.dy + kMargin + offsetInViewport;
-    double dy;
+    double? dy;
     if (caretTop < scrollOffset) {
       dy = caretTop;
     } else if (caretBottom > scrollOffset + viewportHeight) {
@@ -927,9 +927,9 @@ class RenderEditableContainerBox extends RenderBox
   containerNode.Container _container;
   TextDirection textDirection;
   EdgeInsetsGeometry _padding;
-  EdgeInsets _resolvedPadding;
+  EdgeInsets? _resolvedPadding;
 
-  RenderEditableContainerBox(List<RenderEditableBox> children, this._container,
+  RenderEditableContainerBox(List<RenderEditableBox>? children, this._container,
       this.textDirection, this._padding)
       : assert(_container != null),
         assert(textDirection != null),
@@ -963,22 +963,22 @@ class RenderEditableContainerBox extends RenderBox
     _markNeedsPaddingResolution();
   }
 
-  EdgeInsets get resolvedPadding => _resolvedPadding;
+  EdgeInsets? get resolvedPadding => _resolvedPadding;
 
   _resolvePadding() {
     if (_resolvedPadding != null) {
       return;
     }
     _resolvedPadding = _padding.resolve(textDirection);
-    _resolvedPadding = _resolvedPadding.copyWith(left: _resolvedPadding.left);
+    _resolvedPadding = _resolvedPadding!.copyWith(left: _resolvedPadding!.left);
 
-    assert(_resolvedPadding.isNonNegative);
+    assert(_resolvedPadding!.isNonNegative);
   }
 
   RenderEditableBox childAtPosition(TextPosition position) {
     assert(firstChild != null);
 
-    Node targetNode = _container.queryChild(position.offset, false).node;
+    Node? targetNode = _container.queryChild(position.offset, false).node;
 
     var targetChild = firstChild;
     while (targetChild != null) {
@@ -998,19 +998,19 @@ class RenderEditableContainerBox extends RenderBox
     markNeedsLayout();
   }
 
-  RenderEditableBox childAtOffset(Offset offset) {
+  RenderEditableBox? childAtOffset(Offset offset) {
     assert(firstChild != null);
     _resolvePadding();
 
-    if (offset.dy <= _resolvedPadding.top) {
+    if (offset.dy <= _resolvedPadding!.top) {
       return firstChild;
     }
-    if (offset.dy >= size.height - _resolvedPadding.bottom) {
+    if (offset.dy >= size.height - _resolvedPadding!.bottom) {
       return lastChild;
     }
 
     var child = firstChild;
-    double dx = -offset.dx, dy = _resolvedPadding.top;
+    double dx = -offset.dx, dy = _resolvedPadding!.top;
     while (child != null) {
       if (child.size.contains(offset.translate(dx, -dy))) {
         return child;
@@ -1037,20 +1037,20 @@ class RenderEditableContainerBox extends RenderBox
     _resolvePadding();
     assert(_resolvedPadding != null);
 
-    double mainAxisExtent = _resolvedPadding.top;
+    double mainAxisExtent = _resolvedPadding!.top;
     var child = firstChild;
     BoxConstraints innerConstraints =
         BoxConstraints.tightFor(width: constraints.maxWidth)
-            .deflate(_resolvedPadding);
+            .deflate(_resolvedPadding!);
     while (child != null) {
       child.layout(innerConstraints, parentUsesSize: true);
-      final EditableContainerParentData childParentData = child.parentData;
+      final EditableContainerParentData childParentData = child.parentData as EditableContainerParentData;
-      childParentData.offset = Offset(_resolvedPadding.left, mainAxisExtent);
+      childParentData.offset = Offset(_resolvedPadding!.left, mainAxisExtent);
       mainAxisExtent += child.size.height;
       assert(child.parentData == childParentData);
       child = childParentData.nextSibling;
     }
-    mainAxisExtent += _resolvedPadding.bottom;
+    mainAxisExtent += _resolvedPadding!.bottom;
     size = constraints.constrain(Size(constraints.maxWidth, mainAxisExtent));
 
     assert(size.isFinite);
@@ -1061,7 +1061,7 @@ class RenderEditableContainerBox extends RenderBox
     var child = firstChild;
     while (child != null) {
       extent = math.max(extent, childSize(child));
-      EditableContainerParentData childParentData = child.parentData;
+      EditableContainerParentData childParentData = child.parentData as EditableContainerParentData;
       child = childParentData.nextSibling;
     }
     return extent;
@@ -1072,7 +1072,7 @@ class RenderEditableContainerBox extends RenderBox
     var child = firstChild;
     while (child != null) {
       extent += childSize(child);
-      EditableContainerParentData childParentData = child.parentData;
+      EditableContainerParentData childParentData = child.parentData as EditableContainerParentData;
       child = childParentData.nextSibling;
     }
     return extent;
@@ -1083,10 +1083,10 @@ class RenderEditableContainerBox extends RenderBox
     _resolvePadding();
     return _getIntrinsicCrossAxis((RenderBox child) {
       double childHeight = math.max(
-          0.0, height - _resolvedPadding.top + _resolvedPadding.bottom);
+          0.0, height - _resolvedPadding!.top + _resolvedPadding!.bottom);
       return child.getMinIntrinsicWidth(childHeight) +
-          _resolvedPadding.left +
+          _resolvedPadding!.left +
-          _resolvedPadding.right;
+          _resolvedPadding!.right;
     });
   }
 
@@ -1095,10 +1095,10 @@ class RenderEditableContainerBox extends RenderBox
     _resolvePadding();
     return _getIntrinsicCrossAxis((RenderBox child) {
       double childHeight = math.max(
-          0.0, height - _resolvedPadding.top + _resolvedPadding.bottom);
+          0.0, height - _resolvedPadding!.top + _resolvedPadding!.bottom);
       return child.getMaxIntrinsicWidth(childHeight) +
-          _resolvedPadding.left +
+          _resolvedPadding!.left +
-          _resolvedPadding.right;
+          _resolvedPadding!.right;
     });
   }
 
@@ -1107,10 +1107,10 @@ class RenderEditableContainerBox extends RenderBox
     _resolvePadding();
     return _getIntrinsicMainAxis((RenderBox child) {
       double childWidth =
-          math.max(0.0, width - _resolvedPadding.left + _resolvedPadding.right);
+          math.max(0.0, width - _resolvedPadding!.left + _resolvedPadding!.right);
       return child.getMinIntrinsicHeight(childWidth) +
-          _resolvedPadding.top +
+          _resolvedPadding!.top +
-          _resolvedPadding.bottom;
+          _resolvedPadding!.bottom;
     });
   }
 
@@ -1119,17 +1119,17 @@ class RenderEditableContainerBox extends RenderBox
     _resolvePadding();
     return _getIntrinsicMainAxis((RenderBox child) {
       final childWidth =
-          math.max(0.0, width - _resolvedPadding.left + _resolvedPadding.right);
+          math.max(0.0, width - _resolvedPadding!.left + _resolvedPadding!.right);
       return child.getMaxIntrinsicHeight(childWidth) +
-          _resolvedPadding.top +
+          _resolvedPadding!.top +
-          _resolvedPadding.bottom;
+          _resolvedPadding!.bottom;
     });
   }
 
   @override
   double computeDistanceToActualBaseline(TextBaseline baseline) {
     _resolvePadding();
-    return defaultComputeDistanceToFirstActualBaseline(baseline) +
+    return defaultComputeDistanceToFirstActualBaseline(baseline)! +
-        _resolvedPadding.top;
+        _resolvedPadding!.top;
   }
 }

lib/widgets/image.dart

@@ -8,7 +8,7 @@ class ImageTapWrapper extends StatelessWidget {
     this.imageProvider,
   });
 
-  final ImageProvider imageProvider;
+  final ImageProvider? imageProvider;
 
   @override
   Widget build(BuildContext context) {

lib/widgets/keyboard_listener.dart

@@ -4,7 +4,7 @@ enum InputShortcut { CUT, COPY, PASTE, SELECT_ALL }
 
 typedef CursorMoveCallback = void Function(
     LogicalKeyboardKey key, bool wordModifier, bool lineModifier, bool shift);
-typedef InputShortcutCallback = void Function(InputShortcut shortcut);
+typedef InputShortcutCallback = void Function(InputShortcut? shortcut);
 typedef OnDeleteCallback = void Function(bool forward);
 
 class KeyboardListener {

lib/widgets/proxy.dart

@@ -4,17 +4,17 @@ import 'package:flutter/widgets.dart';
 import 'box.dart';
 
 class BaselineProxy extends SingleChildRenderObjectWidget {
-  final TextStyle textStyle;
+  final TextStyle? textStyle;
-  final EdgeInsets padding;
+  final EdgeInsets? padding;
 
-  BaselineProxy({Key key, Widget child, this.textStyle, this.padding})
+  BaselineProxy({Key? key, Widget? child, this.textStyle, this.padding})
       : super(key: key, child: child);
 
   @override
   RenderBaselineProxy createRenderObject(BuildContext context) {
     return RenderBaselineProxy(
       null,
-      textStyle,
+      textStyle!,
       padding,
     );
   }
@@ -23,16 +23,16 @@ class BaselineProxy extends SingleChildRenderObjectWidget {
   void updateRenderObject(
       BuildContext context, covariant RenderBaselineProxy renderObject) {
     renderObject
-      ..textStyle = textStyle
+      ..textStyle = textStyle!
-      ..padding = padding;
+      ..padding = padding!;
   }
 }
 
 class RenderBaselineProxy extends RenderProxyBox {
   RenderBaselineProxy(
-    RenderParagraph child,
+    RenderParagraph? child,
     TextStyle textStyle,
-    EdgeInsets padding,
+    EdgeInsets? padding,
   )   : _prototypePainter = TextPainter(
             text: TextSpan(text: ' ', style: textStyle),
             textDirection: TextDirection.ltr,
@@ -43,18 +43,16 @@ class RenderBaselineProxy extends RenderProxyBox {
   final TextPainter _prototypePainter;
 
   set textStyle(TextStyle value) {
-    assert(value != null);
+    if (_prototypePainter.text!.style == value) {
-    if (_prototypePainter.text.style == value) {
       return;
     }
     _prototypePainter.text = TextSpan(text: ' ', style: value);
     markNeedsLayout();
   }
 
-  EdgeInsets _padding;
+  EdgeInsets? _padding;
 
   set padding(EdgeInsets value) {
-    assert(value != null);
     if (_padding == value) {
       return;
     }
@@ -64,9 +62,8 @@ class RenderBaselineProxy extends RenderProxyBox {
 
   @override
   double computeDistanceToActualBaseline(TextBaseline baseline) =>
-      _prototypePainter.computeDistanceToActualBaseline(baseline) +
+      _prototypePainter.computeDistanceToActualBaseline(baseline);
-          _padding?.top ??
+  // SEE What happens + _padding?.top;
-      0.0;
 
   @override
   performLayout() {
@@ -84,7 +81,7 @@ class EmbedProxy extends SingleChildRenderObjectWidget {
 }
 
 class RenderEmbedProxy extends RenderProxyBox implements RenderContentProxyBox {
-  RenderEmbedProxy(RenderBox child) : super(child);
+  RenderEmbedProxy(RenderBox? child) : super(child);
 
   @override
   List<TextBox> getBoxesForSelection(TextSelection selection) {
@@ -105,10 +102,8 @@ class RenderEmbedProxy extends RenderProxyBox implements RenderContentProxyBox {
   double getFullHeightForCaret(TextPosition position) => size.height;
 
   @override
-  Offset getOffsetForCaret(TextPosition position, Rect caretPrototype) {
+  Offset getOffsetForCaret(TextPosition position, Rect? caretPrototype) {
-    assert(position.offset != null &&
+    assert(position.offset <= 1 && position.offset >= 0);
-        position.offset <= 1 &&
-        position.offset >= 0);
     return position.offset == 0 ? Offset.zero : Offset(size.width, 0.0);
   }
 
@@ -134,7 +129,7 @@ class RichTextProxy extends SingleChildRenderObjectWidget {
   final Locale locale;
   final StrutStyle strutStyle;
   final TextWidthBasis textWidthBasis;
-  final TextHeightBehavior textHeightBehavior;
+  final TextHeightBehavior? textHeightBehavior;
 
   @override
   RenderParagraphProxy createRenderObject(BuildContext context) {
@@ -160,13 +155,7 @@ class RichTextProxy extends SingleChildRenderObjectWidget {
       this.strutStyle,
       this.textWidthBasis,
       this.textHeightBehavior)
-      : assert(child != null),
+      : super(child: child);
-        assert(textStyle != null),
-        assert(textAlign != null),
-        assert(textDirection != null),
-        assert(locale != null),
-        assert(strutStyle != null),
-        super(child: child);
 
   @override
   void updateRenderObject(
@@ -185,7 +174,7 @@ class RichTextProxy extends SingleChildRenderObjectWidget {
 class RenderParagraphProxy extends RenderProxyBox
     implements RenderContentProxyBox {
   RenderParagraphProxy(
-    RenderParagraph child,
+    RenderParagraph? child,
     TextStyle textStyle,
     TextAlign textAlign,
     TextDirection textDirection,
@@ -193,7 +182,7 @@ class RenderParagraphProxy extends RenderProxyBox
     StrutStyle strutStyle,
     Locale locale,
     TextWidthBasis textWidthBasis,
-    TextHeightBehavior textHeightBehavior,
+    TextHeightBehavior? textHeightBehavior,
   )   : _prototypePainter = TextPainter(
             text: TextSpan(text: ' ', style: textStyle),
             textAlign: textAlign,
@@ -208,8 +197,7 @@ class RenderParagraphProxy extends RenderProxyBox
   final TextPainter _prototypePainter;
 
   set textStyle(TextStyle value) {
-    assert(value != null);
+    if (_prototypePainter.text!.style == value) {
-    if (_prototypePainter.text.style == value) {
       return;
     }
     _prototypePainter.text = TextSpan(text: ' ', style: value);
@@ -217,7 +205,6 @@ class RenderParagraphProxy extends RenderProxyBox
   }
 
   set textAlign(TextAlign value) {
-    assert(value != null);
     if (_prototypePainter.textAlign == value) {
       return;
     }
@@ -226,7 +213,6 @@ class RenderParagraphProxy extends RenderProxyBox
   }
 
   set textDirection(TextDirection value) {
-    assert(value != null);
     if (_prototypePainter.textDirection == value) {
       return;
     }
@@ -235,7 +221,6 @@ class RenderParagraphProxy extends RenderProxyBox
   }
 
   set textScaleFactor(double value) {
-    assert(value != null);
     if (_prototypePainter.textScaleFactor == value) {
       return;
     }
@@ -244,7 +229,6 @@ class RenderParagraphProxy extends RenderProxyBox
   }
 
   set strutStyle(StrutStyle value) {
-    assert(value != null);
     if (_prototypePainter.strutStyle == value) {
       return;
     }
@@ -261,7 +245,6 @@ class RenderParagraphProxy extends RenderProxyBox
   }
 
   set textWidthBasis(TextWidthBasis value) {
-    assert(value != null);
     if (_prototypePainter.textWidthBasis == value) {
       return;
     }
@@ -269,7 +252,7 @@ class RenderParagraphProxy extends RenderProxyBox
     markNeedsLayout();
   }
 
-  set textHeightBehavior(TextHeightBehavior value) {
+  set textHeightBehavior(TextHeightBehavior? value) {
     if (_prototypePainter.textHeightBehavior == value) {
       return;
     }
@@ -278,7 +261,7 @@ class RenderParagraphProxy extends RenderProxyBox
   }
 
   @override
-  RenderParagraph get child => super.child;
+  RenderParagraph? get child => super.child as RenderParagraph?;
 
   @override
   double getPreferredLineHeight() {
@@ -286,24 +269,24 @@ class RenderParagraphProxy extends RenderProxyBox
   }
 
   @override
-  Offset getOffsetForCaret(TextPosition position, Rect caretPrototype) =>
+  Offset getOffsetForCaret(TextPosition position, Rect? caretPrototype) =>
-      child.getOffsetForCaret(position, caretPrototype);
+      child!.getOffsetForCaret(position, caretPrototype!);
 
   @override
   TextPosition getPositionForOffset(Offset offset) =>
-      child.getPositionForOffset(offset);
+      child!.getPositionForOffset(offset);
 
   @override
-  double getFullHeightForCaret(TextPosition position) =>
+  double? getFullHeightForCaret(TextPosition position) =>
-      child.getFullHeightForCaret(position);
+      child!.getFullHeightForCaret(position);
 
   @override
   TextRange getWordBoundary(TextPosition position) =>
-      child.getWordBoundary(position);
+      child!.getWordBoundary(position);
 
   @override
   List<TextBox> getBoxesForSelection(TextSelection selection) =>
-      child.getBoxesForSelection(selection);
+      child!.getBoxesForSelection(selection);
 
   @override
   performLayout() {

lib/widgets/raw_editor.dart

@@ -36,23 +36,23 @@ class RawEditor extends StatefulWidget {
   final bool scrollable;
   final EdgeInsetsGeometry padding;
   final bool readOnly;
-  final String placeholder;
+  final String? placeholder;
-  final ValueChanged<String> onLaunchUrl;
+  final ValueChanged<String>? onLaunchUrl;
   final ToolbarOptions toolbarOptions;
   final bool showSelectionHandles;
   final bool showCursor;
   final CursorStyle cursorStyle;
   final TextCapitalization textCapitalization;
-  final double maxHeight;
+  final double? maxHeight;
-  final double minHeight;
+  final double? minHeight;
-  final DefaultStyles customStyles;
+  final DefaultStyles? customStyles;
   final bool expands;
   final bool autoFocus;
   final Color selectionColor;
   final TextSelectionControls selectionCtrls;
   final Brightness keyboardAppearance;
   final bool enableInteractiveSelection;
-  final ScrollPhysics scrollPhysics;
+  final ScrollPhysics? scrollPhysics;
   final EmbedBuilder embedBuilder;
 
   RawEditor(
@@ -67,7 +67,7 @@ class RawEditor extends StatefulWidget {
       this.onLaunchUrl,
       this.toolbarOptions,
       this.showSelectionHandles,
-      bool showCursor,
+      bool? showCursor,
       this.cursorStyle,
       this.textCapitalization,
       this.maxHeight,
@@ -81,26 +81,11 @@ class RawEditor extends StatefulWidget {
       this.enableInteractiveSelection,
       this.scrollPhysics,
       this.embedBuilder)
-      : assert(controller != null, 'controller cannot be null'),
+      : assert(maxHeight == null || maxHeight > 0, 'maxHeight cannot be null'),
-        assert(focusNode != null, 'focusNode cannot be null'),
-        assert(scrollable || scrollController != null,
-            'scrollController cannot be null'),
-        assert(selectionColor != null, 'selectionColor cannot be null'),
-        assert(enableInteractiveSelection != null,
-            'enableInteractiveSelection cannot be null'),
-        assert(showSelectionHandles != null,
-            'showSelectionHandles cannot be null'),
-        assert(readOnly != null, 'readOnly cannot be null'),
-        assert(maxHeight == null || maxHeight > 0, 'maxHeight cannot be null'),
         assert(minHeight == null || minHeight >= 0, 'minHeight cannot be null'),
         assert(maxHeight == null || minHeight == null || maxHeight >= minHeight,
             'maxHeight cannot be null'),
-        assert(autoFocus != null, 'autoFocus cannot be null'),
-        assert(toolbarOptions != null, 'toolbarOptions cannot be null'),
         showCursor = showCursor ?? !readOnly,
-        assert(embedBuilder != null, 'embedBuilder cannot be null'),
-        assert(expands != null, 'expands cannot be null'),
-        assert(padding != null),
         super(key: key);
 
   @override
@@ -117,20 +102,20 @@ class RawEditorState extends EditorState
     implements TextSelectionDelegate, TextInputClient {
   final GlobalKey _editorKey = GlobalKey();
   final List<TextEditingValue> _sentRemoteValues = [];
-  TextInputConnection _textInputConnection;
+  TextInputConnection? _textInputConnection;
-  TextEditingValue _lastKnownRemoteTextEditingValue;
+  TextEditingValue? _lastKnownRemoteTextEditingValue;
   int _cursorResetLocation = -1;
   bool _wasSelectingVerticallyWithKeyboard = false;
-  EditorTextSelectionOverlay _selectionOverlay;
+  EditorTextSelectionOverlay? _selectionOverlay;
-  FocusAttachment _focusAttachment;
+  FocusAttachment? _focusAttachment;
-  CursorCont _cursorCont;
+  late CursorCont _cursorCont;
-  ScrollController _scrollController;
+  ScrollController? _scrollController;
-  KeyboardVisibilityController _keyboardVisibilityController;
+  late KeyboardVisibilityController _keyboardVisibilityController;
-  StreamSubscription<bool> _keyboardVisibilitySubscription;
+  late StreamSubscription<bool> _keyboardVisibilitySubscription;
-  KeyboardListener _keyboardListener;
+  late KeyboardListener _keyboardListener;
   bool _didAutoFocus = false;
   bool _keyboardVisible = false;
-  DefaultStyles _styles;
+  DefaultStyles? _styles;
   final ClipboardStatusNotifier _clipboardStatus = ClipboardStatusNotifier();
   final LayerLink _toolbarLayerLink = LayerLink();
   final LayerLink _startHandleLayerLink = LayerLink();
@@ -140,7 +125,6 @@ class RawEditorState extends EditorState
 
   TextDirection get _textDirection {
     TextDirection result = Directionality.of(context);
-    assert(result != null);
     return result;
   }
 
@@ -154,7 +138,6 @@ class RawEditorState extends EditorState
       return;
     }
     TextSelection selection = widget.controller.selection;
-    assert(selection != null);
 
     TextSelection newSelection = widget.controller.selection;
 
@@ -210,19 +193,20 @@ class RawEditorState extends EditorState
     TextPosition originPosition = TextPosition(
         offset: upKey ? selection.baseOffset : selection.extentOffset);
 
-    RenderEditableBox child = getRenderEditor().childAtPosition(originPosition);
+    RenderEditableBox child =
+        getRenderEditor()!.childAtPosition(originPosition);
     TextPosition localPosition = TextPosition(
         offset:
             originPosition.offset - child.getContainer().getDocumentOffset());
 
-    TextPosition position = upKey
+    TextPosition? position = upKey
         ? child.getPositionAbove(localPosition)
         : child.getPositionBelow(localPosition);
 
     if (position == null) {
       var sibling = upKey
-          ? getRenderEditor().childBefore(child)
+          ? getRenderEditor()!.childBefore(child)
-          : getRenderEditor().childAfter(child);
+          : getRenderEditor()!.childAfter(child);
       if (sibling == null) {
         position = TextPosition(offset: upKey ? 0 : plainText.length - 1);
       } else {
@@ -273,20 +257,20 @@ class RawEditorState extends EditorState
       bool shift) {
     if (wordModifier) {
       if (leftKey) {
-        TextSelection textSelection = getRenderEditor().selectWordAtPosition(
+        TextSelection textSelection = getRenderEditor()!.selectWordAtPosition(
             TextPosition(
                 offset: _previousCharacter(
                     newSelection.extentOffset, plainText, false)));
         return newSelection.copyWith(extentOffset: textSelection.baseOffset);
       }
-      TextSelection textSelection = getRenderEditor().selectWordAtPosition(
+      TextSelection textSelection = getRenderEditor()!.selectWordAtPosition(
           TextPosition(
               offset:
                   _nextCharacter(newSelection.extentOffset, plainText, false)));
       return newSelection.copyWith(extentOffset: textSelection.extentOffset);
     } else if (lineModifier) {
       if (leftKey) {
-        TextSelection textSelection = getRenderEditor().selectLineAtPosition(
+        TextSelection textSelection = getRenderEditor()!.selectLineAtPosition(
             TextPosition(
                 offset: _previousCharacter(
                     newSelection.extentOffset, plainText, false)));
@@ -294,7 +278,7 @@ class RawEditorState extends EditorState
       }
       int startPoint = newSelection.extentOffset;
       if (startPoint < plainText.length) {
-        TextSelection textSelection = getRenderEditor()
+        TextSelection textSelection = getRenderEditor()!
             .selectLineAtPosition(TextPosition(offset: startPoint));
         return newSelection.copyWith(extentOffset: textSelection.extentOffset);
       }
@@ -352,7 +336,7 @@ class RawEditorState extends EditorState
     }
 
     int count = 0;
-    int lastNonWhitespace;
+    int? lastNonWhitespace;
     for (String currentString in string.characters) {
       if (!includeWhitespace &&
           !WHITE_SPACE.contains(
@@ -368,7 +352,7 @@ class RawEditorState extends EditorState
   }
 
   bool get hasConnection =>
-      _textInputConnection != null && _textInputConnection.attached;
+      _textInputConnection != null && _textInputConnection!.attached;
 
   openConnectionIfNeeded() {
     if (widget.readOnly) {
@@ -390,17 +374,17 @@ class RawEditorState extends EditorState
         ),
       );
 
-      _textInputConnection.setEditingState(_lastKnownRemoteTextEditingValue);
+      _textInputConnection!.setEditingState(_lastKnownRemoteTextEditingValue!);
       // _sentRemoteValues.add(_lastKnownRemoteTextEditingValue);
     }
-    _textInputConnection.show();
+    _textInputConnection!.show();
   }
 
   closeConnectionIfNeeded() {
     if (!hasConnection) {
       return;
     }
-    _textInputConnection.close();
+    _textInputConnection!.close();
     _textInputConnection = null;
     _lastKnownRemoteTextEditingValue = null;
     _sentRemoteValues.clear();
@@ -412,7 +396,7 @@ class RawEditorState extends EditorState
     }
 
     TextEditingValue actualValue = textEditingValue.copyWith(
-      composing: _lastKnownRemoteTextEditingValue.composing,
+      composing: _lastKnownRemoteTextEditingValue!.composing,
     );
 
     if (actualValue == _lastKnownRemoteTextEditingValue) {
@@ -420,20 +404,20 @@ class RawEditorState extends EditorState
     }
 
     bool shouldRemember =
-        textEditingValue.text != _lastKnownRemoteTextEditingValue.text;
+        textEditingValue.text != _lastKnownRemoteTextEditingValue!.text;
     _lastKnownRemoteTextEditingValue = actualValue;
-    _textInputConnection.setEditingState(actualValue);
+    _textInputConnection!.setEditingState(actualValue);
     if (shouldRemember) {
       _sentRemoteValues.add(actualValue);
     }
   }
 
   @override
-  TextEditingValue get currentTextEditingValue =>
+  TextEditingValue? get currentTextEditingValue =>
       _lastKnownRemoteTextEditingValue;
 
   @override
-  AutofillScope get currentAutofillScope => null;
+  AutofillScope? get currentAutofillScope => null;
 
   @override
   void updateEditingValue(TextEditingValue value) {
@@ -450,13 +434,14 @@ class RawEditorState extends EditorState
       return;
     }
 
-    if (_lastKnownRemoteTextEditingValue.text == value.text &&
+    if (_lastKnownRemoteTextEditingValue!.text == value.text &&
-        _lastKnownRemoteTextEditingValue.selection == value.selection) {
+        _lastKnownRemoteTextEditingValue!.selection == value.selection) {
       _lastKnownRemoteTextEditingValue = value;
       return;
     }
 
-    TextEditingValue effectiveLastKnownValue = _lastKnownRemoteTextEditingValue;
+    TextEditingValue effectiveLastKnownValue =
+        _lastKnownRemoteTextEditingValue!;
     _lastKnownRemoteTextEditingValue = value;
     String oldText = effectiveLastKnownValue.text;
     String text = value.text;
@@ -500,7 +485,7 @@ class RawEditorState extends EditorState
     if (!hasConnection) {
       return;
     }
-    _textInputConnection.connectionClosedReceived();
+    _textInputConnection!.connectionClosedReceived();
     _textInputConnection = null;
     _lastKnownRemoteTextEditingValue = null;
     _sentRemoteValues.clear();
@@ -509,7 +494,7 @@ class RawEditorState extends EditorState
   @override
   Widget build(BuildContext context) {
     assert(debugCheckHasMediaQuery(context));
-    _focusAttachment.reparent();
+    _focusAttachment!.reparent();
     super.build(context);
 
     Document _doc = widget.controller.document;
@@ -540,9 +525,9 @@ class RawEditorState extends EditorState
 
     if (widget.scrollable) {
       EdgeInsets baselinePadding =
-          EdgeInsets.only(top: _styles.paragraph.verticalSpacing.item1);
+          EdgeInsets.only(top: _styles!.paragraph!.verticalSpacing.item1);
       child = BaselineProxy(
-        textStyle: _styles.paragraph.style,
+        textStyle: _styles!.paragraph!.style,
         padding: baselinePadding,
         child: SingleChildScrollView(
           controller: _scrollController,
@@ -559,7 +544,7 @@ class RawEditorState extends EditorState
             maxHeight: widget.maxHeight ?? double.infinity);
 
     return QuillStyles(
-      data: _styles,
+      data: _styles!,
       child: MouseRegion(
         cursor: SystemMouseCursors.text,
         child: Container(
@@ -620,7 +605,7 @@ class RawEditorState extends EditorState
       line: node,
       textDirection: _textDirection,
       embedBuilder: widget.embedBuilder,
-      styles: _styles,
+      styles: _styles!,
     );
     EditableTextLine editableTextLine = EditableTextLine(
         node,
@@ -639,57 +624,52 @@ class RawEditorState extends EditorState
   }
 
   Tuple2<double, double> _getVerticalSpacingForLine(
-      Line line, DefaultStyles defaultStyles) {
+      Line line, DefaultStyles? defaultStyles) {
     Map<String, Attribute> attrs = line.style.attributes;
     if (attrs.containsKey(Attribute.header.key)) {
-      int level = attrs[Attribute.header.key].value;
+      int? level = attrs[Attribute.header.key]!.value;
       switch (level) {
         case 1:
-          return defaultStyles.h1.verticalSpacing;
+          return defaultStyles!.h1!.verticalSpacing;
         case 2:
-          return defaultStyles.h2.verticalSpacing;
+          return defaultStyles!.h2!.verticalSpacing;
         case 3:
-          return defaultStyles.h3.verticalSpacing;
+          return defaultStyles!.h3!.verticalSpacing;
         default:
           throw ('Invalid level $level');
       }
     }
 
-    return defaultStyles.paragraph.verticalSpacing;
+    return defaultStyles!.paragraph!.verticalSpacing;
   }
 
   Tuple2<double, double> _getVerticalSpacingForBlock(
-      Block node, DefaultStyles defaultStyles) {
+      Block node, DefaultStyles? defaultStyles) {
     Map<String, Attribute> attrs = node.style.attributes;
     if (attrs.containsKey(Attribute.blockQuote.key)) {
-      return defaultStyles.quote.verticalSpacing;
+      return defaultStyles!.quote!.verticalSpacing;
     } else if (attrs.containsKey(Attribute.codeBlock.key)) {
-      return defaultStyles.code.verticalSpacing;
+      return defaultStyles!.code!.verticalSpacing;
     } else if (attrs.containsKey(Attribute.indent.key)) {
-      return defaultStyles.indent.verticalSpacing;
+      return defaultStyles!.indent!.verticalSpacing;
     }
-    return defaultStyles.lists.verticalSpacing;
+    return defaultStyles!.lists!.verticalSpacing;
   }
 
   @override
   void initState() {
     super.initState();
 
-    _clipboardStatus?.addListener(_onChangedClipboardStatus);
+    _clipboardStatus.addListener(_onChangedClipboardStatus);
 
     widget.controller.addListener(_didChangeTextEditingValue);
 
-    _scrollController = widget.scrollController ?? ScrollController();
+    _scrollController = widget.scrollController;
-    _scrollController.addListener(_updateSelectionOverlayForScroll);
+    _scrollController!.addListener(_updateSelectionOverlayForScroll);
 
     _cursorCont = CursorCont(
-      show: ValueNotifier<bool>(widget.showCursor ?? false),
+      show: ValueNotifier<bool>(widget.showCursor),
-      style: widget.cursorStyle ??
+      style: widget.cursorStyle,
-          CursorStyle(
-            color: Colors.blueAccent,
-            backgroundColor: Colors.grey,
-            width: 2.0,
-          ),
       tickerProvider: this,
     );
 
@@ -716,14 +696,14 @@ class RawEditorState extends EditorState
   @override
   didChangeDependencies() {
     super.didChangeDependencies();
-    DefaultStyles parentStyles = QuillStyles.getStyles(context, true);
+    DefaultStyles? parentStyles = QuillStyles.getStyles(context, true);
     DefaultStyles defaultStyles = DefaultStyles.getInstance(context);
     _styles = (parentStyles != null)
         ? defaultStyles.merge(parentStyles)
         : defaultStyles;
 
     if (widget.customStyles != null) {
-      _styles = _styles.merge(widget.customStyles);
+      _styles = _styles!.merge(widget.customStyles!);
     }
 
     if (!_didAutoFocus && widget.autoFocus) {
@@ -745,11 +725,10 @@ class RawEditorState extends EditorState
       updateRemoteValueIfNeeded();
     }
 
-    if (widget.scrollController != null &&
+    if (widget.scrollController != _scrollController) {
-        widget.scrollController != _scrollController) {
+      _scrollController!.removeListener(_updateSelectionOverlayForScroll);
-      _scrollController.removeListener(_updateSelectionOverlayForScroll);
       _scrollController = widget.scrollController;
-      _scrollController.addListener(_updateSelectionOverlayForScroll);
+      _scrollController!.addListener(_updateSelectionOverlayForScroll);
     }
 
     if (widget.focusNode != oldWidget.focusNode) {
@@ -783,7 +762,6 @@ class RawEditorState extends EditorState
   handleDelete(bool forward) {
     TextSelection selection = widget.controller.selection;
     String plainText = textEditingValue.text;
-    assert(selection != null);
     int cursorPosition = selection.start;
     String textBefore = selection.textBefore(plainText);
     String textAfter = selection.textAfter(plainText);
@@ -811,9 +789,8 @@ class RawEditorState extends EditorState
     );
   }
 
-  Future<void> handleShortcut(InputShortcut shortcut) async {
+  void handleShortcut(InputShortcut? shortcut) async {
     TextSelection selection = widget.controller.selection;
-    assert(selection != null);
     String plainText = textEditingValue.text;
     if (shortcut == InputShortcut.COPY) {
       if (!selection.isCollapsed) {
@@ -842,13 +819,13 @@ class RawEditorState extends EditorState
       return;
     }
     if (shortcut == InputShortcut.PASTE && !widget.readOnly) {
-      ClipboardData data = await Clipboard.getData(Clipboard.kTextPlain);
+      ClipboardData? data = await Clipboard.getData(Clipboard.kTextPlain);
       if (data != null) {
         widget.controller.replaceText(
           selection.start,
           selection.end - selection.start,
           data.text,
-          TextSelection.collapsed(offset: selection.start + data.text.length),
+          TextSelection.collapsed(offset: selection.start + data.text!.length),
         );
       }
       return;
@@ -874,10 +851,10 @@ class RawEditorState extends EditorState
     _selectionOverlay = null;
     widget.controller.removeListener(_didChangeTextEditingValue);
     widget.focusNode.removeListener(_handleFocusChanged);
-    _focusAttachment.detach();
+    _focusAttachment!.detach();
     _cursorCont.dispose();
-    _clipboardStatus?.removeListener(_onChangedClipboardStatus);
+    _clipboardStatus.removeListener(_onChangedClipboardStatus);
-    _clipboardStatus?.dispose();
+    _clipboardStatus.dispose();
     super.dispose();
   }
 
@@ -909,7 +886,7 @@ class RawEditorState extends EditorState
       _cursorCont.startCursorTimer();
     }
 
-    SchedulerBinding.instance.addPostFrameCallback(
+    SchedulerBinding.instance!.addPostFrameCallback(
         (Duration _) => _updateOrDisposeSelectionOverlayIfNeeded());
     if (!mounted) return;
     setState(() {
@@ -921,9 +898,9 @@ class RawEditorState extends EditorState
   _updateOrDisposeSelectionOverlayIfNeeded() {
     if (_selectionOverlay != null) {
       if (_hasFocus) {
-        _selectionOverlay.update(textEditingValue);
+        _selectionOverlay!.update(textEditingValue);
       } else {
-        _selectionOverlay.dispose();
+        _selectionOverlay!.dispose();
         _selectionOverlay = null;
       }
     } else if (_hasFocus) {
@@ -945,8 +922,8 @@ class RawEditorState extends EditorState
             DragStartBehavior.start,
             null,
             _clipboardStatus);
-        _selectionOverlay.handlesVisible = _shouldShowSelectionHandles();
+        _selectionOverlay!.handlesVisible = _shouldShowSelectionHandles();
-        _selectionOverlay.showHandles();
+        _selectionOverlay!.showHandles();
       }
     }
   }
@@ -957,10 +934,10 @@ class RawEditorState extends EditorState
         _hasFocus, widget.controller.selection);
     _updateOrDisposeSelectionOverlayIfNeeded();
     if (_hasFocus) {
-      WidgetsBinding.instance.addObserver(this);
+      WidgetsBinding.instance!.addObserver(this);
       _showCaretOnScreen();
     } else {
-      WidgetsBinding.instance.removeObserver(this);
+      WidgetsBinding.instance!.removeObserver(this);
     }
     updateKeepAlive();
   }
@@ -981,23 +958,22 @@ class RawEditorState extends EditorState
     }
 
     _showCaretOnScreenScheduled = true;
-    SchedulerBinding.instance.addPostFrameCallback((Duration _) {
+    SchedulerBinding.instance!.addPostFrameCallback((Duration _) {
       _showCaretOnScreenScheduled = false;
 
-      final viewport = RenderAbstractViewport.of(getRenderEditor());
+      final viewport = RenderAbstractViewport.of(getRenderEditor())!;
-      assert(viewport != null);
+      final editorOffset = getRenderEditor()!
-      final editorOffset =
+          .localToGlobal(Offset(0.0, 0.0), ancestor: viewport);
-          getRenderEditor().localToGlobal(Offset(0.0, 0.0), ancestor: viewport);
+      final offsetInViewport = _scrollController!.offset + editorOffset.dy;
-      final offsetInViewport = _scrollController.offset + editorOffset.dy;
 
-      final offset = getRenderEditor().getOffsetToRevealCursor(
+      final offset = getRenderEditor()!.getOffsetToRevealCursor(
-        _scrollController.position.viewportDimension,
+        _scrollController!.position.viewportDimension,
-        _scrollController.offset,
+        _scrollController!.offset,
         offsetInViewport,
       );
 
       if (offset != null) {
-        _scrollController.animateTo(
+        _scrollController!.animateTo(
           offset,
           duration: Duration(milliseconds: 100),
           curve: Curves.fastOutSlowIn,
@@ -1007,12 +983,12 @@ class RawEditorState extends EditorState
   }
 
   @override
-  RenderEditor getRenderEditor() {
+  RenderEditor? getRenderEditor() {
-    return _editorKey.currentContext.findRenderObject();
+    return _editorKey.currentContext!.findRenderObject() as RenderEditor?;
   }
 
   @override
-  EditorTextSelectionOverlay getSelectionOverlay() {
+  EditorTextSelectionOverlay? getSelectionOverlay() {
     return _selectionOverlay;
   }
 
@@ -1068,7 +1044,7 @@ class RawEditorState extends EditorState
       );
     } else {
       final TextEditingValue value = textEditingValue;
-      final ClipboardData data = await Clipboard.getData(Clipboard.kTextPlain);
+      final ClipboardData? data = await Clipboard.getData(Clipboard.kTextPlain);
       if (data != null) {
         final length =
             textEditingValue.selection.end - textEditingValue.selection.start;
@@ -1081,24 +1057,26 @@ class RawEditorState extends EditorState
         // move cursor to the end of pasted text selection
         widget.controller.updateSelection(
             TextSelection.collapsed(
-                offset: value.selection.start + data.text.length),
+                offset: value.selection.start + data.text!.length),
             ChangeSource.LOCAL);
       }
     }
   }
 
   Future<bool> __isItCut(TextEditingValue value) async {
-    final ClipboardData data = await Clipboard.getData(Clipboard.kTextPlain);
+    final ClipboardData data = await (Clipboard.getData(Clipboard.kTextPlain)
-    return textEditingValue.text.length - value.text.length == data.text.length;
+        as FutureOr<ClipboardData>);
+    return textEditingValue.text.length - value.text.length ==
+        data.text!.length;
   }
 
   @override
   bool showToolbar() {
-    if (_selectionOverlay == null || _selectionOverlay.toolbar != null) {
+    if (_selectionOverlay == null || _selectionOverlay!.toolbar != null) {
       return false;
     }
 
-    _selectionOverlay.showToolbar();
+    _selectionOverlay!.showToolbar();
     return true;
   }
 
@@ -1116,15 +1094,15 @@ class RawEditorState extends EditorState
 
 class _Editor extends MultiChildRenderObjectWidget {
   _Editor({
-    @required Key key,
+    required Key key,
-    @required List<Widget> children,
+    required List<Widget> children,
-    @required this.document,
+    required this.document,
-    @required this.textDirection,
+    required this.textDirection,
-    @required this.hasFocus,
+    required this.hasFocus,
-    @required this.selection,
+    required this.selection,
-    @required this.startHandleLayerLink,
+    required this.startHandleLayerLink,
-    @required this.endHandleLayerLink,
+    required this.endHandleLayerLink,
-    @required this.onSelectionChanged,
+    required this.onSelectionChanged,
     this.padding = EdgeInsets.zero,
   }) : super(key: key, children: children);
 

lib/widgets/responsive_widget.dart

@@ -2,12 +2,12 @@ import 'package:flutter/material.dart';
 
 class ResponsiveWidget extends StatelessWidget {
   final Widget largeScreen;
-  final Widget mediumScreen;
+  final Widget? mediumScreen;
-  final Widget smallScreen;
+  final Widget? smallScreen;
 
   const ResponsiveWidget(
-      {Key key,
+      {Key? key,
-      @required this.largeScreen,
+      required this.largeScreen,
       this.mediumScreen,
       this.smallScreen})
       : super(key: key);

lib/widgets/text_block.dart

@@ -53,10 +53,10 @@ class EditableTextBlock extends StatelessWidget {
   final Tuple2 verticalSpacing;
   final TextSelection textSelection;
   final Color color;
-  final DefaultStyles styles;
+  final DefaultStyles? styles;
   final bool enableInteractiveSelection;
   final bool hasFocus;
-  final EdgeInsets contentPadding;
+  final EdgeInsets? contentPadding;
   final EmbedBuilder embedBuilder;
   final CursorCont cursorCont;
   final Map<int, int> indentLevelCounts;
@@ -82,35 +82,35 @@ class EditableTextBlock extends StatelessWidget {
   Widget build(BuildContext context) {
     assert(debugCheckHasMediaQuery(context));
 
-    DefaultStyles defaultStyles = QuillStyles.getStyles(context, false);
+    DefaultStyles? defaultStyles = QuillStyles.getStyles(context, false);
     return _EditableBlock(
         block,
         textDirection,
-        verticalSpacing,
+        verticalSpacing as Tuple2<double, double>,
         _getDecorationForBlock(block, defaultStyles) ?? BoxDecoration(),
         contentPadding,
         _buildChildren(context, this.indentLevelCounts));
   }
 
-  BoxDecoration _getDecorationForBlock(
+  BoxDecoration? _getDecorationForBlock(
-      Block node, DefaultStyles defaultStyles) {
+      Block node, DefaultStyles? defaultStyles) {
     Map<String, Attribute> attrs = block.style.attributes;
     if (attrs.containsKey(Attribute.blockQuote.key)) {
-      return defaultStyles.quote.decoration;
+      return defaultStyles!.quote!.decoration;
     }
     if (attrs.containsKey(Attribute.codeBlock.key)) {
-      return defaultStyles.code.decoration;
+      return defaultStyles!.code!.decoration;
     }
     return null;
   }
 
   List<Widget> _buildChildren(
       BuildContext context, Map<int, int> indentLevelCounts) {
-    DefaultStyles defaultStyles = QuillStyles.getStyles(context, false);
+    DefaultStyles? defaultStyles = QuillStyles.getStyles(context, false);
     int count = block.children.length;
     var children = <Widget>[];
     int index = 0;
-    for (Line line in block.children) {
+    for (Line line in block.children as Iterable<Line>) {
       index++;
       EditableTextLine editableTextLine = EditableTextLine(
           line,
@@ -119,7 +119,7 @@ class EditableTextBlock extends StatelessWidget {
             line: line,
             textDirection: textDirection,
             embedBuilder: embedBuilder,
-            styles: styles,
+            styles: styles!,
           ),
           _getIndentWidth(),
           _getSpacingForLine(line, index, count, defaultStyles),
@@ -135,16 +135,16 @@ class EditableTextBlock extends StatelessWidget {
     return children.toList(growable: false);
   }
 
-  Widget _buildLeading(BuildContext context, Line line, int index,
+  Widget? _buildLeading(BuildContext context, Line line, int index,
       Map<int, int> indentLevelCounts, int count) {
-    DefaultStyles defaultStyles = QuillStyles.getStyles(context, false);
+    DefaultStyles? defaultStyles = QuillStyles.getStyles(context, false);
     Map<String, Attribute> attrs = line.style.attributes;
     if (attrs[Attribute.list.key] == Attribute.ol) {
       return _NumberPoint(
         index: index,
         indentLevelCounts: indentLevelCounts,
         count: count,
-        style: defaultStyles.paragraph.style,
+        style: defaultStyles!.paragraph!.style,
         attrs: attrs,
         width: 32.0,
         padding: 8.0,
@@ -154,19 +154,19 @@ class EditableTextBlock extends StatelessWidget {
     if (attrs[Attribute.list.key] == Attribute.ul) {
       return _BulletPoint(
         style:
-            defaultStyles.paragraph.style.copyWith(fontWeight: FontWeight.bold),
+            defaultStyles!.paragraph!.style.copyWith(fontWeight: FontWeight.bold),
         width: 32,
       );
     }
 
     if (attrs[Attribute.list.key] == Attribute.checked) {
       return _Checkbox(
-          style: defaultStyles.paragraph.style, width: 32, isChecked: true);
+          style: defaultStyles!.paragraph!.style, width: 32, isChecked: true);
     }
 
     if (attrs[Attribute.list.key] == Attribute.unchecked) {
       return _Checkbox(
-          style: defaultStyles.paragraph.style, width: 32, isChecked: false);
+          style: defaultStyles!.paragraph!.style, width: 32, isChecked: false);
     }
 
     if (attrs.containsKey(Attribute.codeBlock.key)) {
@@ -174,8 +174,8 @@ class EditableTextBlock extends StatelessWidget {
         index: index,
         indentLevelCounts: indentLevelCounts,
         count: count,
-        style: defaultStyles.code.style
+        style: defaultStyles!.code!.style
-            .copyWith(color: defaultStyles.code.style.color.withOpacity(0.4)),
+            .copyWith(color: defaultStyles.code!.style.color!.withOpacity(0.4)),
         width: 32.0,
         attrs: attrs,
         padding: 16.0,
@@ -188,7 +188,7 @@ class EditableTextBlock extends StatelessWidget {
   double _getIndentWidth() {
     Map<String, Attribute> attrs = block.style.attributes;
 
-    Attribute indent = attrs[Attribute.indent.key];
+    Attribute? indent = attrs[Attribute.indent.key];
     double extraIndent = 0.0;
     if (indent != null && indent.value != null) {
       extraIndent = 16.0 * indent.value;
@@ -202,40 +202,40 @@ class EditableTextBlock extends StatelessWidget {
   }
 
   Tuple2 _getSpacingForLine(
-      Line node, int index, int count, DefaultStyles defaultStyles) {
+      Line node, int index, int count, DefaultStyles? defaultStyles) {
     double top = 0.0, bottom = 0.0;
 
     Map<String, Attribute> attrs = block.style.attributes;
     if (attrs.containsKey(Attribute.header.key)) {
-      int level = attrs[Attribute.header.key].value;
+      int? level = attrs[Attribute.header.key]!.value;
       switch (level) {
         case 1:
-          top = defaultStyles.h1.verticalSpacing.item1;
+          top = defaultStyles!.h1!.verticalSpacing.item1;
-          bottom = defaultStyles.h1.verticalSpacing.item2;
+          bottom = defaultStyles.h1!.verticalSpacing.item2;
           break;
         case 2:
-          top = defaultStyles.h2.verticalSpacing.item1;
+          top = defaultStyles!.h2!.verticalSpacing.item1;
-          bottom = defaultStyles.h2.verticalSpacing.item2;
+          bottom = defaultStyles.h2!.verticalSpacing.item2;
           break;
         case 3:
-          top = defaultStyles.h3.verticalSpacing.item1;
+          top = defaultStyles!.h3!.verticalSpacing.item1;
-          bottom = defaultStyles.h3.verticalSpacing.item2;
+          bottom = defaultStyles.h3!.verticalSpacing.item2;
           break;
         default:
           throw ('Invalid level $level');
       }
     } else {
-      Tuple2 lineSpacing;
+      late Tuple2 lineSpacing;
       if (attrs.containsKey(Attribute.blockQuote.key)) {
-        lineSpacing = defaultStyles.quote.lineSpacing;
+        lineSpacing = defaultStyles!.quote!.lineSpacing;
       } else if (attrs.containsKey(Attribute.indent.key)) {
-        lineSpacing = defaultStyles.indent.lineSpacing;
+        lineSpacing = defaultStyles!.indent!.lineSpacing;
       } else if (attrs.containsKey(Attribute.list.key)) {
-        lineSpacing = defaultStyles.lists.lineSpacing;
+        lineSpacing = defaultStyles!.lists!.lineSpacing;
       } else if (attrs.containsKey(Attribute.codeBlock.key)) {
-        lineSpacing = defaultStyles.code.lineSpacing;
+        lineSpacing = defaultStyles!.code!.lineSpacing;
       } else if (attrs.containsKey(Attribute.align.key)) {
-        lineSpacing = defaultStyles.align.lineSpacing;
+        lineSpacing = defaultStyles!.align!.lineSpacing;
       }
       top = lineSpacing.item1;
       bottom = lineSpacing.item2;
@@ -256,11 +256,11 @@ class EditableTextBlock extends StatelessWidget {
 class RenderEditableTextBlock extends RenderEditableContainerBox
     implements RenderEditableBox {
   RenderEditableTextBlock({
-    List<RenderEditableBox> children,
+    List<RenderEditableBox>? children,
-    @required Block block,
+    required Block block,
-    @required TextDirection textDirection,
+    required TextDirection textDirection,
-    @required EdgeInsetsGeometry padding,
+    required EdgeInsetsGeometry padding,
-    @required Decoration decoration,
+    required Decoration decoration,
     ImageConfiguration configuration = ImageConfiguration.empty,
     EdgeInsets contentPadding = EdgeInsets.zero,
   })  : assert(block != null),
@@ -295,7 +295,7 @@ class RenderEditableTextBlock extends RenderEditableContainerBox
     _savedPadding = value;
   }
 
-  BoxPainter _painter;
+  BoxPainter? _painter;
 
   Decoration get decoration => _decoration;
   Decoration _decoration;
@@ -344,8 +344,8 @@ class RenderEditableTextBlock extends RenderEditableContainerBox
 
   @override
   TextPosition getPositionForOffset(Offset offset) {
-    RenderEditableBox child = childAtOffset(offset);
+    RenderEditableBox child = childAtOffset(offset)!;
-    BoxParentData parentData = child.parentData;
+    BoxParentData parentData = child.parentData as BoxParentData;
     TextPosition localPosition =
         child.getPositionForOffset(offset - parentData.offset);
     return TextPosition(
@@ -367,19 +367,19 @@ class RenderEditableTextBlock extends RenderEditableContainerBox
   }
 
   @override
-  TextPosition getPositionAbove(TextPosition position) {
+  TextPosition? getPositionAbove(TextPosition position) {
     assert(position.offset < getContainer().length);
 
     RenderEditableBox child = childAtPosition(position);
     TextPosition childLocalPosition = TextPosition(
         offset: position.offset - child.getContainer().getOffset());
-    TextPosition result = child.getPositionAbove(childLocalPosition);
+    TextPosition? result = child.getPositionAbove(childLocalPosition);
     if (result != null) {
       return TextPosition(
           offset: result.offset + child.getContainer().getOffset());
     }
 
-    RenderEditableBox sibling = childBefore(child);
+    RenderEditableBox? sibling = childBefore(child);
     if (sibling == null) {
       return null;
     }
@@ -395,19 +395,19 @@ class RenderEditableTextBlock extends RenderEditableContainerBox
   }
 
   @override
-  TextPosition getPositionBelow(TextPosition position) {
+  TextPosition? getPositionBelow(TextPosition position) {
     assert(position.offset < getContainer().length);
 
     RenderEditableBox child = childAtPosition(position);
     TextPosition childLocalPosition = TextPosition(
         offset: position.offset - child.getContainer().getOffset());
-    TextPosition result = child.getPositionBelow(childLocalPosition);
+    TextPosition? result = child.getPositionBelow(childLocalPosition);
     if (result != null) {
       return TextPosition(
           offset: result.offset + child.getContainer().getOffset());
     }
 
-    RenderEditableBox sibling = childAfter(child);
+    RenderEditableBox? sibling = childAfter(child);
     if (sibling == null) {
       return null;
     }
@@ -436,7 +436,7 @@ class RenderEditableTextBlock extends RenderEditableContainerBox
           null);
     }
 
-    Node baseNode = getContainer().queryChild(selection.start, false).node;
+    Node? baseNode = getContainer().queryChild(selection.start, false).node;
     var baseChild = firstChild;
     while (baseChild != null) {
       if (baseChild.getContainer() == baseNode) {
@@ -446,7 +446,7 @@ class RenderEditableTextBlock extends RenderEditableContainerBox
     }
     assert(baseChild != null);
 
-    TextSelectionPoint basePoint = baseChild.getBaseEndpointForSelection(
+    TextSelectionPoint basePoint = baseChild!.getBaseEndpointForSelection(
         localSelection(baseChild.getContainer(), selection, true));
     return TextSelectionPoint(
         basePoint.point + (baseChild.parentData as BoxParentData).offset,
@@ -462,7 +462,7 @@ class RenderEditableTextBlock extends RenderEditableContainerBox
           null);
     }
 
-    Node extentNode = getContainer().queryChild(selection.end, false).node;
+    Node? extentNode = getContainer().queryChild(selection.end, false).node;
 
     var extentChild = firstChild;
     while (extentChild != null) {
@@ -473,7 +473,7 @@ class RenderEditableTextBlock extends RenderEditableContainerBox
     }
     assert(extentChild != null);
 
-    TextSelectionPoint extentPoint = extentChild.getExtentEndpointForSelection(
+    TextSelectionPoint extentPoint = extentChild!.getExtentEndpointForSelection(
         localSelection(extentChild.getContainer(), selection, true));
     return TextSelectionPoint(
         extentPoint.point + (extentChild.parentData as BoxParentData).offset,
@@ -499,7 +499,7 @@ class RenderEditableTextBlock extends RenderEditableContainerBox
     assert(size.height != null);
     _painter ??= _decoration.createBoxPainter(markNeedsPaint);
 
-    EdgeInsets decorationPadding = resolvedPadding - _contentPadding;
+    EdgeInsets decorationPadding = resolvedPadding! - _contentPadding;
 
     ImageConfiguration filledConfiguration =
         configuration.copyWith(size: decorationPadding.deflateSize(size));
@@ -507,7 +507,7 @@ class RenderEditableTextBlock extends RenderEditableContainerBox
 
     final decorationOffset =
         offset.translate(decorationPadding.left, decorationPadding.top);
-    _painter.paint(context.canvas, decorationOffset, filledConfiguration);
+    _painter!.paint(context.canvas, decorationOffset, filledConfiguration);
     if (debugSaveCount != context.canvas.getSaveCount()) {
       throw ('${_decoration.runtimeType} painter had mismatching save and restore calls.');
     }
@@ -517,7 +517,7 @@ class RenderEditableTextBlock extends RenderEditableContainerBox
   }
 
   @override
-  bool hitTestChildren(BoxHitTestResult result, {Offset position}) {
+  bool hitTestChildren(BoxHitTestResult result, {required Offset position}) {
     return defaultHitTestChildren(result, position: position);
   }
 }
@@ -527,7 +527,7 @@ class _EditableBlock extends MultiChildRenderObjectWidget {
   final TextDirection textDirection;
   final Tuple2<double, double> padding;
   final Decoration decoration;
-  final EdgeInsets contentPadding;
+  final EdgeInsets? contentPadding;
 
   _EditableBlock(this.block, this.textDirection, this.padding, this.decoration,
       this.contentPadding, List<Widget> children)
@@ -567,7 +567,7 @@ class _EditableBlock extends MultiChildRenderObjectWidget {
 
 class _NumberPoint extends StatelessWidget {
   final int index;
-  final Map<int, int> indentLevelCounts;
+  final Map<int?, int> indentLevelCounts;
   final int count;
   final TextStyle style;
   final double width;
@@ -576,13 +576,13 @@ class _NumberPoint extends StatelessWidget {
   final double padding;
 
   const _NumberPoint({
-    Key key,
+    Key? key,
-    @required this.index,
+    required this.index,
-    @required this.indentLevelCounts,
+    required this.indentLevelCounts,
-    @required this.count,
+    required this.count,
-    @required this.style,
+    required this.style,
-    @required this.width,
+    required this.width,
-    @required this.attrs,
+    required this.attrs,
     this.withDot = true,
     this.padding = 0.0,
   }) : super(key: key);
@@ -590,7 +590,7 @@ class _NumberPoint extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     String s = this.index.toString();
-    int level = 0;
+    int? level = 0;
     if (!this.attrs.containsKey(Attribute.indent.key) &&
         !this.indentLevelCounts.containsKey(1)) {
       this.indentLevelCounts.clear();
@@ -602,13 +602,13 @@ class _NumberPoint extends StatelessWidget {
       );
     }
     if (this.attrs.containsKey(Attribute.indent.key)) {
-      level = this.attrs[Attribute.indent.key].value;
+      level = this.attrs[Attribute.indent.key]!.value;
     } else {
       // first level but is back from previous indent level
       // supposed to be "2."
       this.indentLevelCounts[0] = 1;
     }
-    if (this.indentLevelCounts.containsKey(level + 1)) {
+    if (this.indentLevelCounts.containsKey(level! + 1)) {
       // last visited level is done, going up
       this.indentLevelCounts.remove(level + 1);
     }
@@ -674,9 +674,9 @@ class _BulletPoint extends StatelessWidget {
   final double width;
 
   const _BulletPoint({
-    Key key,
+    Key? key,
-    @required this.style,
+    required this.style,
-    @required this.width,
+    required this.width,
   }) : super(key: key);
 
   @override
@@ -691,23 +691,23 @@ class _BulletPoint extends StatelessWidget {
 }
 
 class _Checkbox extends StatefulWidget {
-  final TextStyle style;
+  final TextStyle? style;
-  final double width;
+  final double? width;
-  final bool isChecked;
+  final bool? isChecked;
 
-  const _Checkbox({Key key, this.style, this.width, this.isChecked})
+  const _Checkbox({Key? key, this.style, this.width, this.isChecked})
       : super(key: key);
   @override
   __CheckboxState createState() => __CheckboxState();
 }
 
 class __CheckboxState extends State<_Checkbox> {
-  bool isChecked;
+  bool? isChecked;
 
-  void _onCheckboxClicked(bool newValue) => setState(() {
+  void _onCheckboxClicked(bool? newValue) => setState(() {
         isChecked = newValue;
 
-        if (isChecked) {
+        if (isChecked!) {
           // check list
         } else {
           // uncheck list

lib/widgets/text_line.dart

@@ -23,16 +23,17 @@ import 'delegate.dart';
 
 class TextLine extends StatelessWidget {
   final Line line;
-  final TextDirection textDirection;
+  final TextDirection? textDirection;
   final EmbedBuilder embedBuilder;
   final DefaultStyles styles;
 
   const TextLine(
-      {Key key, this.line, this.textDirection, this.embedBuilder, this.styles})
+      {Key? key,
-      : assert(line != null),
+      required this.line,
-        assert(embedBuilder != null),
+      this.textDirection,
-        assert(styles != null),
+      required this.embedBuilder,
-        super(key: key);
+      required this.styles})
+      : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -45,7 +46,7 @@ class TextLine extends StatelessWidget {
 
     TextSpan textSpan = _buildTextSpan(context);
     StrutStyle strutStyle =
-        StrutStyle.fromTextStyle(textSpan.style, forceStrutHeight: true);
+        StrutStyle.fromTextStyle(textSpan.style!, forceStrutHeight: true);
     final textAlign = _getTextAlign();
     RichText child = RichText(
       text: TextSpan(children: [textSpan]),
@@ -56,9 +57,9 @@ class TextLine extends StatelessWidget {
     );
     return RichTextProxy(
         child,
-        textSpan.style,
+        textSpan.style!,
         textAlign,
-        textDirection,
+        textDirection!,
         1.0,
         Localizations.localeOf(context),
         strutStyle,
@@ -89,27 +90,27 @@ class TextLine extends StatelessWidget {
     TextStyle textStyle = TextStyle();
 
     if (line.style.containsKey(Attribute.placeholder.key)) {
-      textStyle = defaultStyles.placeHolder.style;
+      textStyle = defaultStyles.placeHolder!.style;
       return TextSpan(children: children, style: textStyle);
     }
 
-    Attribute header = line.style.attributes[Attribute.header.key];
+    Attribute? header = line.style.attributes[Attribute.header.key];
     Map<Attribute, TextStyle> m = {
-      Attribute.h1: defaultStyles.h1.style,
+      Attribute.h1: defaultStyles.h1!.style,
-      Attribute.h2: defaultStyles.h2.style,
+      Attribute.h2: defaultStyles.h2!.style,
-      Attribute.h3: defaultStyles.h3.style,
+      Attribute.h3: defaultStyles.h3!.style,
     };
 
-    textStyle = textStyle.merge(m[header] ?? defaultStyles.paragraph.style);
+    textStyle = textStyle.merge(m[header!] ?? defaultStyles.paragraph!.style);
 
-    Attribute block = line.style.getBlockExceptHeader();
+    Attribute? block = line.style.getBlockExceptHeader();
-    TextStyle toMerge;
+    TextStyle? toMerge;
     if (block == Attribute.blockQuote) {
-      toMerge = defaultStyles.quote.style;
+      toMerge = defaultStyles.quote!.style;
     } else if (block == Attribute.codeBlock) {
-      toMerge = defaultStyles.code.style;
+      toMerge = defaultStyles.code!.style;
     } else if (block != null) {
-      toMerge = defaultStyles.lists.style;
+      toMerge = defaultStyles.lists!.style;
     }
 
     textStyle = textStyle.merge(toMerge);
@@ -122,7 +123,7 @@ class TextLine extends StatelessWidget {
     Style style = textNode.style;
     TextStyle res = TextStyle();
 
-    Map<String, TextStyle> m = {
+    Map<String, TextStyle?> m = {
       Attribute.bold.key: defaultStyles.bold,
       Attribute.italic.key: defaultStyles.italic,
       Attribute.link.key: defaultStyles.link,
@@ -131,16 +132,16 @@ class TextLine extends StatelessWidget {
     };
     m.forEach((k, s) {
       if (style.values.any((v) => v.key == k)) {
-        res = _merge(res, s);
+        res = _merge(res, s!);
       }
     });
 
-    Attribute font = textNode.style.attributes[Attribute.font.key];
+    Attribute? font = textNode.style.attributes[Attribute.font.key];
     if (font != null && font.value != null) {
       res = res.merge(TextStyle(fontFamily: font.value));
     }
 
-    Attribute size = textNode.style.attributes[Attribute.size.key];
+    Attribute? size = textNode.style.attributes[Attribute.size.key];
     if (size != null && size.value != null) {
       switch (size.value) {
         case 'small':
@@ -153,7 +154,7 @@ class TextLine extends StatelessWidget {
           res = res.merge(defaultStyles.sizeHuge);
           break;
         default:
-          double fontSize = double.tryParse(size.value);
+          double? fontSize = double.tryParse(size.value);
           if (fontSize != null) {
             res = res.merge(TextStyle(fontSize: fontSize));
           } else {
@@ -162,13 +163,13 @@ class TextLine extends StatelessWidget {
       }
     }
 
-    Attribute color = textNode.style.attributes[Attribute.color.key];
+    Attribute? color = textNode.style.attributes[Attribute.color.key];
     if (color != null && color.value != null) {
       final textColor = stringToColor(color.value);
       res = res.merge(new TextStyle(color: textColor));
     }
 
-    Attribute background = textNode.style.attributes[Attribute.background.key];
+    Attribute? background = textNode.style.attributes[Attribute.background.key];
     if (background != null && background.value != null) {
       final backgroundColor = stringToColor(background.value);
       res = res.merge(new TextStyle(backgroundColor: backgroundColor));
@@ -178,20 +179,22 @@ class TextLine extends StatelessWidget {
   }
 
   TextStyle _merge(TextStyle a, TextStyle b) {
-    final decorations = <TextDecoration>[];
+    final decorations = <TextDecoration?>[];
     if (a.decoration != null) {
       decorations.add(a.decoration);
     }
     if (b.decoration != null) {
       decorations.add(b.decoration);
     }
-    return a.merge(b).apply(decoration: TextDecoration.combine(decorations));
+    return a.merge(b).apply(
+        decoration:
+            TextDecoration.combine(decorations as List<TextDecoration>));
   }
 }
 
 class EditableTextLine extends RenderObjectWidget {
   final Line line;
-  final Widget leading;
+  final Widget? leading;
   final Widget body;
   final double indentWidth;
   final Tuple2 verticalSpacing;
@@ -215,14 +218,7 @@ class EditableTextLine extends RenderObjectWidget {
       this.enableInteractiveSelection,
       this.hasFocus,
       this.devicePixelRatio,
-      this.cursorCont)
+      this.cursorCont);
-      : assert(line != null),
-        assert(indentWidth != null),
-        assert(textSelection != null),
-        assert(color != null),
-        assert(enableInteractiveSelection != null),
-        assert(hasFocus != null),
-        assert(cursorCont != null);
 
   @override
   RenderObjectElement createElement() {
@@ -268,8 +264,8 @@ class EditableTextLine extends RenderObjectWidget {
 enum TextLineSlot { LEADING, BODY }
 
 class RenderEditableTextLine extends RenderEditableBox {
-  RenderBox _leading;
+  RenderBox? _leading;
-  RenderContentProxyBox _body;
+  RenderContentProxyBox? _body;
   Line line;
   TextDirection textDirection;
   TextSelection textSelection;
@@ -279,10 +275,10 @@ class RenderEditableTextLine extends RenderEditableBox {
   double devicePixelRatio;
   EdgeInsetsGeometry padding;
   CursorCont cursorCont;
-  EdgeInsets _resolvedPadding;
+  EdgeInsets? _resolvedPadding;
-  bool _containsCursor;
+  bool? _containsCursor;
-  List<TextBox> _selectedRects;
+  List<TextBox>? _selectedRects;
-  Rect _caretPrototype;
+  Rect? _caretPrototype;
   final Map<TextLineSlot, RenderBox> children = <TextLineSlot, RenderBox>{};
 
   RenderEditableTextLine(
@@ -294,26 +290,18 @@ class RenderEditableTextLine extends RenderEditableBox {
       this.devicePixelRatio,
       this.padding,
       this.color,
-      this.cursorCont)
+      this.cursorCont);
-      : assert(line != null),
-        assert(padding != null),
-        assert(padding.isNonNegative),
-        assert(devicePixelRatio != null),
-        assert(hasFocus != null),
-        assert(color != null),
-        assert(cursorCont != null);
 
   Iterable<RenderBox> get _children sync* {
     if (_leading != null) {
-      yield _leading;
+      yield _leading!;
     }
     if (_body != null) {
-      yield _body;
+      yield _body!;
     }
   }
 
   setCursorCont(CursorCont c) {
-    assert(c != null);
     if (cursorCont == c) {
       return;
     }
@@ -383,7 +371,6 @@ class RenderEditableTextLine extends RenderEditableBox {
   }
 
   setLine(Line l) {
-    assert(l != null);
     if (line == l) {
       return;
     }
@@ -393,7 +380,6 @@ class RenderEditableTextLine extends RenderEditableBox {
   }
 
   setPadding(EdgeInsetsGeometry p) {
-    assert(p != null);
     assert(p.isNonNegative);
     if (padding == p) {
       return;
@@ -403,12 +389,12 @@ class RenderEditableTextLine extends RenderEditableBox {
     markNeedsLayout();
   }
 
-  setLeading(RenderBox l) {
+  setLeading(RenderBox? l) {
     _leading = _updateChild(_leading, l, TextLineSlot.LEADING);
   }
 
-  setBody(RenderContentProxyBox b) {
+  setBody(RenderContentProxyBox? b) {
-    _body = _updateChild(_body, b, TextLineSlot.BODY);
+    _body = _updateChild(_body, b, TextLineSlot.BODY) as RenderContentProxyBox?;
   }
 
   bool containsTextSelection() {
@@ -421,7 +407,8 @@ class RenderEditableTextLine extends RenderEditableBox {
         line.containsOffset(textSelection.baseOffset);
   }
 
-  RenderBox _updateChild(RenderBox old, RenderBox newChild, TextLineSlot slot) {
+  RenderBox? _updateChild(
+      RenderBox? old, RenderBox? newChild, TextLineSlot slot) {
     if (old != null) {
       dropChild(old);
       children.remove(slot);
@@ -434,10 +421,10 @@ class RenderEditableTextLine extends RenderEditableBox {
   }
 
   List<TextBox> _getBoxes(TextSelection textSelection) {
-    BoxParentData parentData = _body.parentData as BoxParentData;
+    BoxParentData? parentData = _body!.parentData as BoxParentData?;
-    return _body.getBoxesForSelection(textSelection).map((box) {
+    return _body!.getBoxesForSelection(textSelection).map((box) {
       return TextBox.fromLTRBD(
-        box.left + parentData.offset.dx,
+        box.left + parentData!.offset.dx,
         box.top + parentData.offset.dy,
         box.right + parentData.offset.dx,
         box.bottom + parentData.offset.dy,
@@ -451,7 +438,7 @@ class RenderEditableTextLine extends RenderEditableBox {
       return;
     }
     _resolvedPadding = padding.resolve(textDirection);
-    assert(_resolvedPadding.isNonNegative);
+    assert(_resolvedPadding!.isNonNegative);
   }
 
   @override
@@ -498,26 +485,26 @@ class RenderEditableTextLine extends RenderEditableBox {
 
   @override
   Offset getOffsetForCaret(TextPosition position) {
-    return _body.getOffsetForCaret(position, _caretPrototype) +
+    return _body!.getOffsetForCaret(position, _caretPrototype) +
-        (_body.parentData as BoxParentData).offset;
+        (_body!.parentData as BoxParentData).offset;
   }
 
   @override
-  TextPosition getPositionAbove(TextPosition position) {
+  TextPosition? getPositionAbove(TextPosition position) {
     return _getPosition(position, -0.5);
   }
 
   @override
-  TextPosition getPositionBelow(TextPosition position) {
+  TextPosition? getPositionBelow(TextPosition position) {
     return _getPosition(position, 1.5);
   }
 
-  TextPosition _getPosition(TextPosition textPosition, double dyScale) {
+  TextPosition? _getPosition(TextPosition textPosition, double dyScale) {
     assert(textPosition.offset < line.length);
     Offset offset = getOffsetForCaret(textPosition)
         .translate(0, dyScale * preferredLineHeight(textPosition));
-    if (_body.size
+    if (_body!.size
-        .contains(offset - (_body.parentData as BoxParentData).offset)) {
+        .contains(offset - (_body!.parentData as BoxParentData).offset)) {
       return getPositionForOffset(offset);
     }
     return null;
@@ -525,18 +512,18 @@ class RenderEditableTextLine extends RenderEditableBox {
 
   @override
   TextPosition getPositionForOffset(Offset offset) {
-    return _body.getPositionForOffset(
+    return _body!.getPositionForOffset(
-        offset - (_body.parentData as BoxParentData).offset);
+        offset - (_body!.parentData as BoxParentData).offset);
   }
 
   @override
   TextRange getWordBoundary(TextPosition position) {
-    return _body.getWordBoundary(position);
+    return _body!.getWordBoundary(position);
   }
 
   @override
   double preferredLineHeight(TextPosition position) {
-    return _body.getPreferredLineHeight();
+    return _body!.getPreferredLineHeight();
   }
 
   @override
@@ -550,7 +537,6 @@ class RenderEditableTextLine extends RenderEditableBox {
       cursorCont.style.height ?? preferredLineHeight(TextPosition(offset: 0));
 
   _computeCaretPrototype() {
-    assert(defaultTargetPlatform != null);
     switch (defaultTargetPlatform) {
       case TargetPlatform.iOS:
       case TargetPlatform.macOS:
@@ -606,7 +592,7 @@ class RenderEditableTextLine extends RenderEditableBox {
   @override
   List<DiagnosticsNode> debugDescribeChildren() {
     var value = <DiagnosticsNode>[];
-    void add(RenderBox child, String name) {
+    void add(RenderBox? child, String name) {
       if (child != null) {
         value.add(child.toDiagnosticsNode(name: name));
       }
@@ -623,38 +609,40 @@ class RenderEditableTextLine extends RenderEditableBox {
   @override
   double computeMinIntrinsicWidth(double height) {
     _resolvePadding();
-    double horizontalPadding = _resolvedPadding.left + _resolvedPadding.right;
+    double horizontalPadding = _resolvedPadding!.left + _resolvedPadding!.right;
-    double verticalPadding = _resolvedPadding.top + _resolvedPadding.bottom;
+    double verticalPadding = _resolvedPadding!.top + _resolvedPadding!.bottom;
     int leadingWidth = _leading == null
         ? 0
-        : _leading.getMinIntrinsicWidth(height - verticalPadding);
+        : _leading!.getMinIntrinsicWidth(height - verticalPadding) as int;
     int bodyWidth = _body == null
         ? 0
-        : _body.getMinIntrinsicWidth(math.max(0.0, height - verticalPadding));
+        : _body!.getMinIntrinsicWidth(math.max(0.0, height - verticalPadding))
+            as int;
     return horizontalPadding + leadingWidth + bodyWidth;
   }
 
   @override
   double computeMaxIntrinsicWidth(double height) {
     _resolvePadding();
-    double horizontalPadding = _resolvedPadding.left + _resolvedPadding.right;
+    double horizontalPadding = _resolvedPadding!.left + _resolvedPadding!.right;
-    double verticalPadding = _resolvedPadding.top + _resolvedPadding.bottom;
+    double verticalPadding = _resolvedPadding!.top + _resolvedPadding!.bottom;
     int leadingWidth = _leading == null
         ? 0
-        : _leading.getMaxIntrinsicWidth(height - verticalPadding);
+        : _leading!.getMaxIntrinsicWidth(height - verticalPadding) as int;
     int bodyWidth = _body == null
         ? 0
-        : _body.getMaxIntrinsicWidth(math.max(0.0, height - verticalPadding));
+        : _body!.getMaxIntrinsicWidth(math.max(0.0, height - verticalPadding))
+            as int;
     return horizontalPadding + leadingWidth + bodyWidth;
   }
 
   @override
   double computeMinIntrinsicHeight(double width) {
     _resolvePadding();
-    double horizontalPadding = _resolvedPadding.left + _resolvedPadding.right;
+    double horizontalPadding = _resolvedPadding!.left + _resolvedPadding!.right;
-    double verticalPadding = _resolvedPadding.top + _resolvedPadding.bottom;
+    double verticalPadding = _resolvedPadding!.top + _resolvedPadding!.bottom;
     if (_body != null) {
-      return _body
+      return _body!
               .getMinIntrinsicHeight(math.max(0.0, width - horizontalPadding)) +
           verticalPadding;
     }
@@ -664,10 +652,10 @@ class RenderEditableTextLine extends RenderEditableBox {
   @override
   double computeMaxIntrinsicHeight(double width) {
     _resolvePadding();
-    double horizontalPadding = _resolvedPadding.left + _resolvedPadding.right;
+    double horizontalPadding = _resolvedPadding!.left + _resolvedPadding!.right;
-    double verticalPadding = _resolvedPadding.top + _resolvedPadding.bottom;
+    double verticalPadding = _resolvedPadding!.top + _resolvedPadding!.bottom;
     if (_body != null) {
-      return _body
+      return _body!
               .getMaxIntrinsicHeight(math.max(0.0, width - horizontalPadding)) +
           verticalPadding;
     }
@@ -677,7 +665,8 @@ class RenderEditableTextLine extends RenderEditableBox {
   @override
   double computeDistanceToActualBaseline(TextBaseline baseline) {
     _resolvePadding();
-    return _body.getDistanceToActualBaseline(baseline) + _resolvedPadding.top;
+    return _body!.getDistanceToActualBaseline(baseline)! +
+        _resolvedPadding!.top;
   }
 
   @override
@@ -690,34 +679,35 @@ class RenderEditableTextLine extends RenderEditableBox {
 
     if (_body == null && _leading == null) {
       size = constraints.constrain(Size(
-        _resolvedPadding.left + _resolvedPadding.right,
+        _resolvedPadding!.left + _resolvedPadding!.right,
-        _resolvedPadding.top + _resolvedPadding.bottom,
+        _resolvedPadding!.top + _resolvedPadding!.bottom,
       ));
       return;
     }
-    final innerConstraints = constraints.deflate(_resolvedPadding);
+    final innerConstraints = constraints.deflate(_resolvedPadding!);
 
     final indentWidth = textDirection == TextDirection.ltr
-        ? _resolvedPadding.left
+        ? _resolvedPadding!.left
-        : _resolvedPadding.right;
+        : _resolvedPadding!.right;
 
-    _body.layout(innerConstraints, parentUsesSize: true);
+    _body!.layout(innerConstraints, parentUsesSize: true);
-    final bodyParentData = _body.parentData as BoxParentData;
+    final bodyParentData = _body!.parentData as BoxParentData;
-    bodyParentData.offset = Offset(_resolvedPadding.left, _resolvedPadding.top);
+    bodyParentData.offset =
+        Offset(_resolvedPadding!.left, _resolvedPadding!.top);
 
     if (_leading != null) {
       final leadingConstraints = innerConstraints.copyWith(
           minWidth: indentWidth,
           maxWidth: indentWidth,
-          maxHeight: _body.size.height);
+          maxHeight: _body!.size.height);
-      _leading.layout(leadingConstraints, parentUsesSize: true);
+      _leading!.layout(leadingConstraints, parentUsesSize: true);
-      final parentData = _leading.parentData as BoxParentData;
+      final parentData = _leading!.parentData as BoxParentData;
-      parentData.offset = Offset(0.0, _resolvedPadding.top);
+      parentData.offset = Offset(0.0, _resolvedPadding!.top);
     }
 
     size = constraints.constrain(Size(
-      _resolvedPadding.left + _body.size.width + _resolvedPadding.right,
+      _resolvedPadding!.left + _body!.size.width + _resolvedPadding!.right,
-      _resolvedPadding.top + _body.size.height + _resolvedPadding.bottom,
+      _resolvedPadding!.top + _body!.size.height + _resolvedPadding!.bottom,
     ));
 
     _computeCaretPrototype();
@@ -734,19 +724,19 @@ class RenderEditableTextLine extends RenderEditableBox {
   @override
   paint(PaintingContext context, Offset offset) {
     if (_leading != null) {
-      final parentData = _leading.parentData as BoxParentData;
+      final parentData = _leading!.parentData as BoxParentData;
       final effectiveOffset = offset + parentData.offset;
-      context.paintChild(_leading, effectiveOffset);
+      context.paintChild(_leading!, effectiveOffset);
     }
 
     if (_body != null) {
-      final parentData = _body.parentData as BoxParentData;
+      final parentData = _body!.parentData as BoxParentData;
       final effectiveOffset = offset + parentData.offset;
-      if ((enableInteractiveSelection ?? true) &&
+      if ((enableInteractiveSelection) &&
           line.getDocumentOffset() <= textSelection.end &&
           textSelection.start <= line.getDocumentOffset() + line.length - 1) {
         final local = localSelection(line, textSelection, false);
-        _selectedRects ??= _body.getBoxesForSelection(
+        _selectedRects ??= _body!.getBoxesForSelection(
           local,
         );
         _paintSelection(context, effectiveOffset);
@@ -759,7 +749,7 @@ class RenderEditableTextLine extends RenderEditableBox {
         _paintCursor(context, effectiveOffset);
       }
 
-      context.paintChild(_body, effectiveOffset);
+      context.paintChild(_body!, effectiveOffset);
 
       if (hasFocus &&
           cursorCont.show.value &&
@@ -773,7 +763,7 @@ class RenderEditableTextLine extends RenderEditableBox {
   _paintSelection(PaintingContext context, Offset effectiveOffset) {
     assert(_selectedRects != null);
     final paint = Paint()..color = color;
-    for (final box in _selectedRects) {
+    for (final box in _selectedRects!) {
       context.canvas.drawRect(box.toRect().shift(effectiveOffset), paint);
     }
   }
@@ -814,7 +804,7 @@ class _TextLineElement extends RenderObjectElement {
   }
 
   @override
-  mount(Element parent, dynamic newSlot) {
+  mount(Element? parent, dynamic newSlot) {
     super.mount(parent, newSlot);
     _mountChild(widget.leading, TextLineSlot.LEADING);
     _mountChild(widget.body, TextLineSlot.BODY);
@@ -829,16 +819,16 @@ class _TextLineElement extends RenderObjectElement {
   }
 
   @override
-  insertRenderObjectChild(RenderObject child, TextLineSlot slot) {
+  insertRenderObjectChild(RenderObject child, TextLineSlot? slot) {
     assert(child is RenderBox);
     _updateRenderObject(child, slot);
     assert(renderObject.children.keys.contains(slot));
   }
 
   @override
-  removeRenderObjectChild(RenderObject child, TextLineSlot slot) {
+  removeRenderObjectChild(RenderObject child, TextLineSlot? slot) {
     assert(child is RenderBox);
-    assert(renderObject.children[slot] == child);
+    assert(renderObject.children[slot!] == child);
     _updateRenderObject(null, slot);
     assert(!renderObject.children.keys.contains(slot));
   }
@@ -848,9 +838,9 @@ class _TextLineElement extends RenderObjectElement {
     throw UnimplementedError();
   }
 
-  _mountChild(Widget widget, TextLineSlot slot) {
+  _mountChild(Widget? widget, TextLineSlot slot) {
-    Element oldChild = _slotToChildren[slot];
+    Element? oldChild = _slotToChildren[slot];
-    Element newChild = updateChild(oldChild, widget, slot);
+    Element? newChild = updateChild(oldChild, widget, slot);
     if (oldChild != null) {
       _slotToChildren.remove(slot);
     }
@@ -859,22 +849,22 @@ class _TextLineElement extends RenderObjectElement {
     }
   }
 
-  _updateRenderObject(RenderObject child, TextLineSlot slot) {
+  _updateRenderObject(RenderObject? child, TextLineSlot? slot) {
     switch (slot) {
       case TextLineSlot.LEADING:
-        renderObject.setLeading(child as RenderBox);
+        renderObject.setLeading(child as RenderBox?);
         break;
       case TextLineSlot.BODY:
-        renderObject.setBody(child as RenderBox);
+        renderObject.setBody((child as RenderBox?) as RenderContentProxyBox?);
         break;
       default:
         throw UnimplementedError();
     }
   }
 
-  _updateChild(Widget widget, TextLineSlot slot) {
+  _updateChild(Widget? widget, TextLineSlot slot) {
-    Element oldChild = _slotToChildren[slot];
+    Element? oldChild = _slotToChildren[slot];
-    Element newChild = updateChild(oldChild, widget, slot);
+    Element? newChild = updateChild(oldChild, widget, slot);
     if (oldChild != null) {
       _slotToChildren.remove(slot);
     }

lib/widgets/text_selection.dart

@@ -31,15 +31,15 @@ class EditorTextSelectionOverlay {
   final LayerLink toolbarLayerLink;
   final LayerLink startHandleLayerLink;
   final LayerLink endHandleLayerLink;
-  final RenderEditor renderObject;
+  final RenderEditor? renderObject;
   final TextSelectionControls selectionCtrls;
   final TextSelectionDelegate selectionDelegate;
   final DragStartBehavior dragStartBehavior;
-  final VoidCallback onSelectionHandleTapped;
+  final VoidCallback? onSelectionHandleTapped;
   final ClipboardStatusNotifier clipboardStatus;
-  AnimationController _toolbarController;
+  late AnimationController _toolbarController;
-  List<OverlayEntry> _handles;
+  List<OverlayEntry>? _handles;
-  OverlayEntry toolbar;
+  OverlayEntry? toolbar;
 
   EditorTextSelectionOverlay(
       this.value,
@@ -58,7 +58,7 @@ class EditorTextSelectionOverlay {
       : assert(value != null),
         assert(context != null),
         assert(handlesVisible != null) {
-    OverlayState overlay = Overlay.of(context, rootOverlay: true);
+    OverlayState overlay = Overlay.of(context, rootOverlay: true)!;
     assert(
       overlay != null,
     );
@@ -76,9 +76,9 @@ class EditorTextSelectionOverlay {
       return;
     }
     handlesVisible = visible;
-    if (SchedulerBinding.instance.schedulerPhase ==
+    if (SchedulerBinding.instance!.schedulerPhase ==
         SchedulerPhase.persistentCallbacks) {
-      SchedulerBinding.instance.addPostFrameCallback(markNeedsBuild);
+      SchedulerBinding.instance!.addPostFrameCallback(markNeedsBuild);
     } else {
       markNeedsBuild();
     }
@@ -88,23 +88,23 @@ class EditorTextSelectionOverlay {
     if (_handles == null) {
       return;
     }
-    _handles[0].remove();
+    _handles![0].remove();
-    _handles[1].remove();
+    _handles![1].remove();
     _handles = null;
   }
 
   hideToolbar() {
     assert(toolbar != null);
     _toolbarController.stop();
-    toolbar.remove();
+    toolbar!.remove();
     toolbar = null;
   }
 
   showToolbar() {
     assert(toolbar == null);
     toolbar = OverlayEntry(builder: _buildToolbar);
-    Overlay.of(context, rootOverlay: true, debugRequiredFor: debugRequiredFor)
+    Overlay.of(context, rootOverlay: true, debugRequiredFor: debugRequiredFor)!
-        .insert(toolbar);
+        .insert(toolbar!);
     _toolbarController.forward(from: 0.0);
   }
 
@@ -118,7 +118,7 @@ class EditorTextSelectionOverlay {
     return Visibility(
         visible: handlesVisible,
         child: _TextSelectionHandleOverlay(
-          onSelectionHandleChanged: (TextSelection newSelection) {
+          onSelectionHandleChanged: (TextSelection? newSelection) {
             _handleSelectionHandleChanged(newSelection, position);
           },
           onSelectionHandleTapped: onSelectionHandleTapped,
@@ -137,23 +137,26 @@ class EditorTextSelectionOverlay {
       return;
     }
     value = newValue;
-    if (SchedulerBinding.instance.schedulerPhase ==
+    if (SchedulerBinding.instance!.schedulerPhase ==
         SchedulerPhase.persistentCallbacks) {
-      SchedulerBinding.instance.addPostFrameCallback(markNeedsBuild);
+      SchedulerBinding.instance!.addPostFrameCallback(markNeedsBuild);
     } else {
       markNeedsBuild();
     }
   }
 
   _handleSelectionHandleChanged(
-      TextSelection newSelection, _TextSelectionHandlePosition position) {
+      TextSelection? newSelection, _TextSelectionHandlePosition position) {
     TextPosition textPosition;
     switch (position) {
       case _TextSelectionHandlePosition.START:
-        textPosition = newSelection.base;
+        textPosition =
+            newSelection != null ? newSelection.base : TextPosition(offset: 0);
         break;
       case _TextSelectionHandlePosition.END:
-        textPosition = newSelection.extent;
+        textPosition = newSelection != null
+            ? newSelection.extent
+            : TextPosition(offset: 0);
         break;
       default:
         throw ('Invalid position');
@@ -169,16 +172,16 @@ class EditorTextSelectionOverlay {
     }
 
     List<TextSelectionPoint> endpoints =
-        renderObject.getEndpointsForSelection(_selection);
+        renderObject!.getEndpointsForSelection(_selection);
 
     Rect editingRegion = Rect.fromPoints(
-      renderObject.localToGlobal(Offset.zero),
+      renderObject!.localToGlobal(Offset.zero),
-      renderObject.localToGlobal(renderObject.size.bottomRight(Offset.zero)),
+      renderObject!.localToGlobal(renderObject!.size.bottomRight(Offset.zero)),
     );
 
-    double baseLineHeight = renderObject.preferredLineHeight(_selection.base);
+    double baseLineHeight = renderObject!.preferredLineHeight(_selection.base);
     double extentLineHeight =
-        renderObject.preferredLineHeight(_selection.extent);
+        renderObject!.preferredLineHeight(_selection.extent);
     double smallestLineHeight = math.min(baseLineHeight, extentLineHeight);
     bool isMultiline = endpoints.last.point.dy - endpoints.first.point.dy >
         smallestLineHeight / 2;
@@ -211,18 +214,18 @@ class EditorTextSelectionOverlay {
     );
   }
 
-  markNeedsBuild([Duration duration]) {
+  markNeedsBuild([Duration? duration]) {
     if (_handles != null) {
-      _handles[0].markNeedsBuild();
+      _handles![0].markNeedsBuild();
-      _handles[1].markNeedsBuild();
+      _handles![1].markNeedsBuild();
     }
     toolbar?.markNeedsBuild();
   }
 
   hide() {
     if (_handles != null) {
-      _handles[0].remove();
+      _handles![0].remove();
-      _handles[1].remove();
+      _handles![1].remove();
       _handles = null;
     }
     if (toolbar != null) {
@@ -246,22 +249,22 @@ class EditorTextSelectionOverlay {
               _buildHandle(context, _TextSelectionHandlePosition.END)),
     ];
 
-    Overlay.of(context, rootOverlay: true, debugRequiredFor: debugRequiredFor)
+    Overlay.of(context, rootOverlay: true, debugRequiredFor: debugRequiredFor)!
-        .insertAll(_handles);
+        .insertAll(_handles!);
   }
 }
 
 class _TextSelectionHandleOverlay extends StatefulWidget {
   const _TextSelectionHandleOverlay({
-    Key key,
+    Key? key,
-    @required this.selection,
+    required this.selection,
-    @required this.position,
+    required this.position,
-    @required this.startHandleLayerLink,
+    required this.startHandleLayerLink,
-    @required this.endHandleLayerLink,
+    required this.endHandleLayerLink,
-    @required this.renderObject,
+    required this.renderObject,
-    @required this.onSelectionHandleChanged,
+    required this.onSelectionHandleChanged,
-    @required this.onSelectionHandleTapped,
+    required this.onSelectionHandleTapped,
-    @required this.selectionControls,
+    required this.selectionControls,
     this.dragStartBehavior = DragStartBehavior.start,
   }) : super(key: key);
 
@@ -269,9 +272,9 @@ class _TextSelectionHandleOverlay extends StatefulWidget {
   final _TextSelectionHandlePosition position;
   final LayerLink startHandleLayerLink;
   final LayerLink endHandleLayerLink;
-  final RenderEditor renderObject;
+  final RenderEditor? renderObject;
-  final ValueChanged<TextSelection> onSelectionHandleChanged;
+  final ValueChanged<TextSelection?> onSelectionHandleChanged;
-  final VoidCallback onSelectionHandleTapped;
+  final VoidCallback? onSelectionHandleTapped;
   final TextSelectionControls selectionControls;
   final DragStartBehavior dragStartBehavior;
 
@@ -279,12 +282,12 @@ class _TextSelectionHandleOverlay extends StatefulWidget {
   _TextSelectionHandleOverlayState createState() =>
       _TextSelectionHandleOverlayState();
 
-  ValueListenable<bool> get _visibility {
+  ValueListenable<bool>? get _visibility {
     switch (position) {
       case _TextSelectionHandlePosition.START:
-        return renderObject.selectionStartInViewport;
+        return renderObject!.selectionStartInViewport;
       case _TextSelectionHandlePosition.END:
-        return renderObject.selectionEndInViewport;
+        return renderObject!.selectionEndInViewport;
     }
     return null;
   }
@@ -293,7 +296,7 @@ class _TextSelectionHandleOverlay extends StatefulWidget {
 class _TextSelectionHandleOverlayState
     extends State<_TextSelectionHandleOverlay>
     with SingleTickerProviderStateMixin {
-  AnimationController _controller;
+  late AnimationController _controller;
 
   Animation<double> get _opacity => _controller.view;
 
@@ -305,11 +308,11 @@ class _TextSelectionHandleOverlayState
         AnimationController(duration: Duration(milliseconds: 150), vsync: this);
 
     _handleVisibilityChanged();
-    widget._visibility.addListener(_handleVisibilityChanged);
+    widget._visibility!.addListener(_handleVisibilityChanged);
   }
 
   _handleVisibilityChanged() {
-    if (widget._visibility.value) {
+    if (widget._visibility!.value) {
       _controller.forward();
     } else {
       _controller.reverse();
@@ -319,14 +322,14 @@ class _TextSelectionHandleOverlayState
   @override
   didUpdateWidget(_TextSelectionHandleOverlay oldWidget) {
     super.didUpdateWidget(oldWidget);
-    oldWidget._visibility.removeListener(_handleVisibilityChanged);
+    oldWidget._visibility!.removeListener(_handleVisibilityChanged);
     _handleVisibilityChanged();
-    widget._visibility.addListener(_handleVisibilityChanged);
+    widget._visibility!.addListener(_handleVisibilityChanged);
   }
 
   @override
   void dispose() {
-    widget._visibility.removeListener(_handleVisibilityChanged);
+    widget._visibility!.removeListener(_handleVisibilityChanged);
     _controller.dispose();
     super.dispose();
   }
@@ -335,7 +338,7 @@ class _TextSelectionHandleOverlayState
 
   _handleDragUpdate(DragUpdateDetails details) {
     TextPosition position =
-        widget.renderObject.getPositionForOffset(details.globalPosition);
+        widget.renderObject!.getPositionForOffset(details.globalPosition);
     if (widget.selection.isCollapsed) {
       widget.onSelectionHandleChanged(TextSelection.fromPosition(position));
       return;
@@ -343,7 +346,7 @@ class _TextSelectionHandleOverlayState
 
     bool isNormalized =
         widget.selection.extentOffset >= widget.selection.baseOffset;
-    TextSelection newSelection;
+    TextSelection? newSelection;
     switch (widget.position) {
       case _TextSelectionHandlePosition.START:
         newSelection = TextSelection(
@@ -368,19 +371,19 @@ class _TextSelectionHandleOverlayState
 
   _handleTap() {
     if (widget.onSelectionHandleTapped != null)
-      widget.onSelectionHandleTapped();
+      widget.onSelectionHandleTapped!();
   }
 
   @override
   Widget build(BuildContext context) {
-    LayerLink layerLink;
+    late LayerLink layerLink;
-    TextSelectionHandleType type;
+    TextSelectionHandleType? type;
 
     switch (widget.position) {
       case _TextSelectionHandlePosition.START:
         layerLink = widget.startHandleLayerLink;
         type = _chooseType(
-          widget.renderObject.textDirection,
+          widget.renderObject!.textDirection,
           TextSelectionHandleType.left,
           TextSelectionHandleType.right,
         );
@@ -389,7 +392,7 @@ class _TextSelectionHandleOverlayState
         assert(!widget.selection.isCollapsed);
         layerLink = widget.endHandleLayerLink;
         type = _chooseType(
-          widget.renderObject.textDirection,
+          widget.renderObject!.textDirection,
           TextSelectionHandleType.right,
           TextSelectionHandleType.left,
         );
@@ -400,9 +403,9 @@ class _TextSelectionHandleOverlayState
         widget.position == _TextSelectionHandlePosition.START
             ? widget.selection.base
             : widget.selection.extent;
-    double lineHeight = widget.renderObject.preferredLineHeight(textPosition);
+    double lineHeight = widget.renderObject!.preferredLineHeight(textPosition);
     Offset handleAnchor =
-        widget.selectionControls.getHandleAnchor(type, lineHeight);
+        widget.selectionControls.getHandleAnchor(type!, lineHeight);
     Size handleSize = widget.selectionControls.getHandleSize(lineHeight);
 
     Rect handleRect = Rect.fromLTWH(
@@ -458,7 +461,7 @@ class _TextSelectionHandleOverlayState
     );
   }
 
-  TextSelectionHandleType _chooseType(
+  TextSelectionHandleType? _chooseType(
     TextDirection textDirection,
     TextSelectionHandleType ltrType,
     TextSelectionHandleType rtlType,
@@ -478,7 +481,7 @@ class _TextSelectionHandleOverlayState
 
 class EditorTextSelectionGestureDetector extends StatefulWidget {
   const EditorTextSelectionGestureDetector({
-    Key key,
+    Key? key,
     this.onTapDown,
     this.onForcePressStart,
     this.onForcePressEnd,
@@ -492,35 +495,35 @@ class EditorTextSelectionGestureDetector extends StatefulWidget {
     this.onDragSelectionUpdate,
     this.onDragSelectionEnd,
     this.behavior,
-    @required this.child,
+    required this.child,
   })   : assert(child != null),
         super(key: key);
 
-  final GestureTapDownCallback onTapDown;
+  final GestureTapDownCallback? onTapDown;
 
-  final GestureForcePressStartCallback onForcePressStart;
+  final GestureForcePressStartCallback? onForcePressStart;
 
-  final GestureForcePressEndCallback onForcePressEnd;
+  final GestureForcePressEndCallback? onForcePressEnd;
 
-  final GestureTapUpCallback onSingleTapUp;
+  final GestureTapUpCallback? onSingleTapUp;
 
-  final GestureTapCancelCallback onSingleTapCancel;
+  final GestureTapCancelCallback? onSingleTapCancel;
 
-  final GestureLongPressStartCallback onSingleLongTapStart;
+  final GestureLongPressStartCallback? onSingleLongTapStart;
 
-  final GestureLongPressMoveUpdateCallback onSingleLongTapMoveUpdate;
+  final GestureLongPressMoveUpdateCallback? onSingleLongTapMoveUpdate;
 
-  final GestureLongPressEndCallback onSingleLongTapEnd;
+  final GestureLongPressEndCallback? onSingleLongTapEnd;
 
-  final GestureTapDownCallback onDoubleTapDown;
+  final GestureTapDownCallback? onDoubleTapDown;
 
-  final GestureDragStartCallback onDragSelectionStart;
+  final GestureDragStartCallback? onDragSelectionStart;
 
-  final DragSelectionUpdateCallback onDragSelectionUpdate;
+  final DragSelectionUpdateCallback? onDragSelectionUpdate;
 
-  final GestureDragEndCallback onDragSelectionEnd;
+  final GestureDragEndCallback? onDragSelectionEnd;
 
-  final HitTestBehavior behavior;
+  final HitTestBehavior? behavior;
 
   final Widget child;
 
@@ -531,8 +534,8 @@ class EditorTextSelectionGestureDetector extends StatefulWidget {
 
 class _EditorTextSelectionGestureDetectorState
     extends State<EditorTextSelectionGestureDetector> {
-  Timer _doubleTapTimer;
+  Timer? _doubleTapTimer;
-  Offset _lastTapOffset;
+  Offset? _lastTapOffset;
   bool _isDoubleTap = false;
 
   @override
@@ -544,15 +547,15 @@ class _EditorTextSelectionGestureDetectorState
 
   _handleTapDown(TapDownDetails details) {
     if (widget.onTapDown != null) {
-      widget.onTapDown(details);
+      widget.onTapDown!(details);
     }
     if (_doubleTapTimer != null &&
         _isWithinDoubleTapTolerance(details.globalPosition)) {
       if (widget.onDoubleTapDown != null) {
-        widget.onDoubleTapDown(details);
+        widget.onDoubleTapDown!(details);
       }
 
-      _doubleTapTimer.cancel();
+      _doubleTapTimer!.cancel();
       _doubleTapTimeout();
       _isDoubleTap = true;
     }
@@ -561,7 +564,7 @@ class _EditorTextSelectionGestureDetectorState
   _handleTapUp(TapUpDetails details) {
     if (!_isDoubleTap) {
       if (widget.onSingleTapUp != null) {
-        widget.onSingleTapUp(details);
+        widget.onSingleTapUp!(details);
       }
       _lastTapOffset = details.globalPosition;
       _doubleTapTimer = Timer(kDoubleTapTimeout, _doubleTapTimeout);
@@ -571,19 +574,19 @@ class _EditorTextSelectionGestureDetectorState
 
   _handleTapCancel() {
     if (widget.onSingleTapCancel != null) {
-      widget.onSingleTapCancel();
+      widget.onSingleTapCancel!();
     }
   }
 
-  DragStartDetails _lastDragStartDetails;
+  DragStartDetails? _lastDragStartDetails;
-  DragUpdateDetails _lastDragUpdateDetails;
+  DragUpdateDetails? _lastDragUpdateDetails;
-  Timer _dragUpdateThrottleTimer;
+  Timer? _dragUpdateThrottleTimer;
 
   _handleDragStart(DragStartDetails details) {
     assert(_lastDragStartDetails == null);
     _lastDragStartDetails = details;
     if (widget.onDragSelectionStart != null) {
-      widget.onDragSelectionStart(details);
+      widget.onDragSelectionStart!(details);
     }
   }
 
@@ -597,8 +600,8 @@ class _EditorTextSelectionGestureDetectorState
     assert(_lastDragStartDetails != null);
     assert(_lastDragUpdateDetails != null);
     if (widget.onDragSelectionUpdate != null) {
-      widget.onDragSelectionUpdate(
+      widget.onDragSelectionUpdate!(
-          _lastDragStartDetails, _lastDragUpdateDetails);
+          _lastDragStartDetails!, _lastDragUpdateDetails!);
     }
     _dragUpdateThrottleTimer = null;
     _lastDragUpdateDetails = null;
@@ -607,11 +610,11 @@ class _EditorTextSelectionGestureDetectorState
   _handleDragEnd(DragEndDetails details) {
     assert(_lastDragStartDetails != null);
     if (_dragUpdateThrottleTimer != null) {
-      _dragUpdateThrottleTimer.cancel();
+      _dragUpdateThrottleTimer!.cancel();
       _handleDragUpdateThrottled();
     }
     if (widget.onDragSelectionEnd != null) {
-      widget.onDragSelectionEnd(details);
+      widget.onDragSelectionEnd!(details);
     }
     _dragUpdateThrottleTimer = null;
     _lastDragStartDetails = null;
@@ -622,31 +625,31 @@ class _EditorTextSelectionGestureDetectorState
     _doubleTapTimer?.cancel();
     _doubleTapTimer = null;
     if (widget.onForcePressStart != null) {
-      widget.onForcePressStart(details);
+      widget.onForcePressStart!(details);
     }
   }
 
   _forcePressEnded(ForcePressDetails details) {
     if (widget.onForcePressEnd != null) {
-      widget.onForcePressEnd(details);
+      widget.onForcePressEnd!(details);
     }
   }
 
   _handleLongPressStart(LongPressStartDetails details) {
     if (!_isDoubleTap && widget.onSingleLongTapStart != null) {
-      widget.onSingleLongTapStart(details);
+      widget.onSingleLongTapStart!(details);
     }
   }
 
   _handleLongPressMoveUpdate(LongPressMoveUpdateDetails details) {
     if (!_isDoubleTap && widget.onSingleLongTapMoveUpdate != null) {
-      widget.onSingleLongTapMoveUpdate(details);
+      widget.onSingleLongTapMoveUpdate!(details);
     }
   }
 
   _handleLongPressEnd(LongPressEndDetails details) {
     if (!_isDoubleTap && widget.onSingleLongTapEnd != null) {
-      widget.onSingleLongTapEnd(details);
+      widget.onSingleLongTapEnd!(details);
     }
     _isDoubleTap = false;
   }
@@ -662,7 +665,7 @@ class _EditorTextSelectionGestureDetectorState
       return false;
     }
 
-    return (secondTapOffset - _lastTapOffset).distance <= kDoubleTapSlop;
+    return (secondTapOffset - _lastTapOffset!).distance <= kDoubleTapSlop;
   }
 
   @override
@@ -738,7 +741,7 @@ class _EditorTextSelectionGestureDetectorState
 
 class _TransparentTapGestureRecognizer extends TapGestureRecognizer {
   _TransparentTapGestureRecognizer({
-    Object debugOwner,
+    Object? debugOwner,
   }) : super(debugOwner: debugOwner);
 
   @override

lib/widgets/toolbar.dart

@@ -23,9 +23,9 @@ class InsertEmbedButton extends StatelessWidget {
   final IconData icon;
 
   const InsertEmbedButton({
-    Key key,
+    Key? key,
-    @required this.controller,
+    required this.controller,
-    @required this.icon,
+    required this.icon,
   }) : super(key: key);
 
   @override
@@ -51,11 +51,11 @@ class InsertEmbedButton extends StatelessWidget {
 
 class LinkStyleButton extends StatefulWidget {
   final QuillController controller;
-  final IconData icon;
+  final IconData? icon;
 
   const LinkStyleButton({
-    Key key,
+    Key? key,
-    @required this.controller,
+    required this.controller,
     this.icon,
   }) : super(key: key);
 
@@ -117,7 +117,7 @@ class _LinkStyleButtonState extends State<LinkStyleButton> {
     ).then(_linkSubmitted);
   }
 
-  void _linkSubmitted(String value) {
+  void _linkSubmitted(String? value) {
     if (value == null || value.isEmpty) {
       return;
     }
@@ -126,7 +126,7 @@ class _LinkStyleButtonState extends State<LinkStyleButton> {
 }
 
 class _LinkDialog extends StatefulWidget {
-  const _LinkDialog({Key key}) : super(key: key);
+  const _LinkDialog({Key? key}) : super(key: key);
 
   @override
   _LinkDialogState createState() => _LinkDialogState();
@@ -167,8 +167,8 @@ typedef ToggleStyleButtonBuilder = Widget Function(
   BuildContext context,
   Attribute attribute,
   IconData icon,
-  bool isToggled,
+  bool? isToggled,
-  VoidCallback onPressed,
+  VoidCallback? onPressed,
 );
 
 class ToggleStyleButton extends StatefulWidget {
@@ -181,10 +181,10 @@ class ToggleStyleButton extends StatefulWidget {
   final ToggleStyleButtonBuilder childBuilder;
 
   ToggleStyleButton({
-    Key key,
+    Key? key,
-    @required this.attribute,
+    required this.attribute,
-    @required this.icon,
+    required this.icon,
-    @required this.controller,
+    required this.controller,
     this.childBuilder = defaultToggleStyleButtonBuilder,
   })  : assert(attribute.value != null),
         assert(icon != null),
@@ -197,7 +197,7 @@ class ToggleStyleButton extends StatefulWidget {
 }
 
 class _ToggleStyleButtonState extends State<ToggleStyleButton> {
-  bool _isToggled;
+  bool? _isToggled;
 
   Style get _selectionStyle => widget.controller.getSelectionStyle();
 
@@ -217,7 +217,7 @@ class _ToggleStyleButtonState extends State<ToggleStyleButton> {
 
   bool _getIsToggled(Map<String, Attribute> attrs) {
     if (widget.attribute.key == Attribute.list.key) {
-      Attribute attribute = attrs[widget.attribute.key];
+      Attribute? attribute = attrs[widget.attribute.key];
       if (attribute == null) {
         return false;
       }
@@ -253,7 +253,7 @@ class _ToggleStyleButtonState extends State<ToggleStyleButton> {
   }
 
   _toggleAttribute() {
-    widget.controller.formatSelection(_isToggled
+    widget.controller.formatSelection(_isToggled!
         ? Attribute.clone(widget.attribute, null)
         : widget.attribute);
   }
@@ -269,11 +269,11 @@ class ToggleCheckListButton extends StatefulWidget {
   final Attribute attribute;
 
   ToggleCheckListButton({
-    Key key,
+    Key? key,
-    @required this.icon,
+    required this.icon,
-    @required this.controller,
+    required this.controller,
     this.childBuilder = defaultToggleStyleButtonBuilder,
-    @required this.attribute,
+    required this.attribute,
   })  : assert(icon != null),
         assert(controller != null),
         assert(childBuilder != null),
@@ -284,7 +284,7 @@ class ToggleCheckListButton extends StatefulWidget {
 }
 
 class _ToggleCheckListButtonState extends State<ToggleCheckListButton> {
-  bool _isToggled;
+  bool? _isToggled;
 
   Style get _selectionStyle => widget.controller.getSelectionStyle();
 
@@ -304,7 +304,7 @@ class _ToggleCheckListButtonState extends State<ToggleCheckListButton> {
 
   bool _getIsToggled(Map<String, Attribute> attrs) {
     if (widget.attribute.key == Attribute.list.key) {
-      Attribute attribute = attrs[widget.attribute.key];
+      Attribute? attribute = attrs[widget.attribute.key];
       if (attribute == null) {
         return false;
       }
@@ -341,7 +341,7 @@ class _ToggleCheckListButtonState extends State<ToggleCheckListButton> {
   }
 
   _toggleAttribute() {
-    widget.controller.formatSelection(_isToggled
+    widget.controller.formatSelection(_isToggled!
         ? Attribute.clone(Attribute.unchecked, null)
         : Attribute.unchecked);
   }
@@ -351,17 +351,17 @@ Widget defaultToggleStyleButtonBuilder(
   BuildContext context,
   Attribute attribute,
   IconData icon,
-  bool isToggled,
+  bool? isToggled,
-  VoidCallback onPressed,
+  VoidCallback? onPressed,
 ) {
   final theme = Theme.of(context);
   final isEnabled = onPressed != null;
   final iconColor = isEnabled
-      ? isToggled
+      ? isToggled != null
           ? theme.primaryIconTheme.color
           : theme.iconTheme.color
       : theme.disabledColor;
-  final fillColor = isToggled ? theme.toggleableActiveColor : theme.canvasColor;
+  final fillColor = isToggled != null ? theme.toggleableActiveColor : theme.canvasColor;
   return QuillIconButton(
     highlightElevation: 0,
     hoverElevation: 0,
@@ -375,7 +375,7 @@ Widget defaultToggleStyleButtonBuilder(
 class SelectHeaderStyleButton extends StatefulWidget {
   final QuillController controller;
 
-  const SelectHeaderStyleButton({Key key, @required this.controller})
+  const SelectHeaderStyleButton({Key? key, required this.controller})
       : super(key: key);
 
   @override
@@ -384,7 +384,7 @@ class SelectHeaderStyleButton extends StatefulWidget {
 }
 
 class _SelectHeaderStyleButtonState extends State<SelectHeaderStyleButton> {
-  Attribute _value;
+  Attribute? _value;
 
   Style get _selectionStyle => widget.controller.getSelectionStyle();
 
@@ -433,7 +433,7 @@ class _SelectHeaderStyleButtonState extends State<SelectHeaderStyleButton> {
 }
 
 Widget _selectHeadingStyleButtonBuilder(
-    BuildContext context, Attribute value, ValueChanged<Attribute> onSelected) {
+    BuildContext context, Attribute? value, ValueChanged<Attribute?> onSelected) {
   final style = TextStyle(fontSize: 13);
 
   final Map<Attribute, String> _valueToText = {
@@ -443,42 +443,42 @@ Widget _selectHeadingStyleButtonBuilder(
     Attribute.h3: 'Heading 3',
   };
 
-  return QuillDropdownButton<Attribute>(
+  return QuillDropdownButton<Attribute?>(
     highlightElevation: 0,
     hoverElevation: 0,
     height: iconSize * 1.77,
     fillColor: Theme.of(context).canvasColor,
     child: Text(
       !kIsWeb
-          ? _valueToText[value]
+          ? _valueToText[value!]!
-          : _valueToText[value.key == "header"
+          : _valueToText[value!.key == "header"
               ? Attribute.header
               : (value.key == "h1")
                   ? Attribute.h1
                   : (value.key == "h2")
                       ? Attribute.h2
-                      : Attribute.h3],
+                      : Attribute.h3]!,
       style: TextStyle(fontSize: 13, fontWeight: FontWeight.w600),
     ),
     initialValue: value,
     items: [
       PopupMenuItem(
-        child: Text(_valueToText[Attribute.header], style: style),
+        child: Text(_valueToText[Attribute.header]!, style: style),
         value: Attribute.header,
         height: iconSize * 1.77,
       ),
       PopupMenuItem(
-        child: Text(_valueToText[Attribute.h1], style: style),
+        child: Text(_valueToText[Attribute.h1]!, style: style),
         value: Attribute.h1,
         height: iconSize * 1.77,
       ),
       PopupMenuItem(
-        child: Text(_valueToText[Attribute.h2], style: style),
+        child: Text(_valueToText[Attribute.h2]!, style: style),
         value: Attribute.h2,
         height: iconSize * 1.77,
       ),
       PopupMenuItem(
-        child: Text(_valueToText[Attribute.h3], style: style),
+        child: Text(_valueToText[Attribute.h3]!, style: style),
         value: Attribute.h3,
         height: iconSize * 1.77,
       ),
@@ -492,15 +492,15 @@ class ImageButton extends StatefulWidget {
 
   final QuillController controller;
 
-  final OnImagePickCallback onImagePickCallback;
+  final OnImagePickCallback? onImagePickCallback;
 
   final ImageSource imageSource;
 
   ImageButton(
-      {Key key,
+      {Key? key,
-      @required this.icon,
+      required this.icon,
-      @required this.controller,
+      required this.controller,
-      @required this.imageSource,
+      required this.imageSource,
       this.onImagePickCallback})
       : assert(icon != null),
         assert(controller != null),
@@ -511,13 +511,13 @@ class ImageButton extends StatefulWidget {
 }
 
 class _ImageButtonState extends State<ImageButton> {
-  List<PlatformFile> _paths;
+  List<PlatformFile>? _paths;
-  String _extension;
+  String? _extension;
   final _picker = ImagePicker();
   FileType _pickingType = FileType.any;
 
-  Future<String> _pickImage(ImageSource source) async {
+  Future<String?> _pickImage(ImageSource source) async {
-    final PickedFile pickedFile = await _picker.getImage(source: source);
+    final PickedFile? pickedFile = await _picker.getImage(source: source);
     if (pickedFile == null) return null;
 
     final File file = File(pickedFile.path);
@@ -525,7 +525,7 @@ class _ImageButtonState extends State<ImageButton> {
     if (file == null || widget.onImagePickCallback == null) return null;
     // We simply return the absolute path to selected file.
     try {
-      String url = await widget.onImagePickCallback(file);
+      String url = await widget.onImagePickCallback!(file);
       print('Image uploaded and its url is $url');
       return url;
     } catch (error) {
@@ -534,13 +534,13 @@ class _ImageButtonState extends State<ImageButton> {
     return null;
   }
 
-  Future<String> _pickImageWeb() async {
+  Future<String?> _pickImageWeb() async {
     try {
       _paths = (await FilePicker.platform.pickFiles(
         type: _pickingType,
         allowMultiple: false,
         allowedExtensions: (_extension?.isNotEmpty ?? false)
-            ? _extension?.replaceAll(' ', '')?.split(',')
+            ? _extension?.replaceAll(' ', '').split(',')
             : null,
       ))
           ?.files;
@@ -550,14 +550,14 @@ class _ImageButtonState extends State<ImageButton> {
       print(ex);
     }
     var _fileName =
-        _paths != null ? _paths.map((e) => e.name).toString() : '...';
+        _paths != null ? _paths!.map((e) => e.name).toString() : '...';
 
     if (_paths != null) {
       File file = File(_fileName);
       if (file == null || widget.onImagePickCallback == null) return null;
       // We simply return the absolute path to selected file.
       try {
-        String url = await widget.onImagePickCallback(file);
+        String url = await widget.onImagePickCallback!(file);
         print('Image uploaded and its url is $url');
         return url;
       } catch (error) {
@@ -607,10 +607,10 @@ class ColorButton extends StatefulWidget {
   final QuillController controller;
 
   ColorButton(
-      {Key key,
+      {Key? key,
-      @required this.icon,
+      required this.icon,
-      @required this.controller,
+      required this.controller,
-      @required this.background})
+      required this.background})
       : assert(icon != null),
         assert(controller != null),
         assert(background != null),
@@ -621,10 +621,10 @@ class ColorButton extends StatefulWidget {
 }
 
 class _ColorButtonState extends State<ColorButton> {
-  bool _isToggledColor;
+  late bool _isToggledColor;
-  bool _isToggledBackground;
+  late bool _isToggledBackground;
-  bool _isWhite;
+  late bool _isWhite;
-  bool _isWhitebackground;
+  late bool _isWhitebackground;
 
   Style get _selectionStyle => widget.controller.getSelectionStyle();
 
@@ -635,9 +635,9 @@ class _ColorButtonState extends State<ColorButton> {
       _isToggledBackground = _getIsToggledBackground(
           widget.controller.getSelectionStyle().attributes);
       _isWhite = _isToggledColor &&
-          _selectionStyle.attributes["color"].value == '#ffffff';
+          _selectionStyle.attributes["color"]!.value == '#ffffff';
       _isWhitebackground = _isToggledBackground &&
-          _selectionStyle.attributes["background"].value == '#ffffff';
+          _selectionStyle.attributes["background"]!.value == '#ffffff';
     });
   }
 
@@ -647,9 +647,9 @@ class _ColorButtonState extends State<ColorButton> {
     _isToggledColor = _getIsToggledColor(_selectionStyle.attributes);
     _isToggledBackground = _getIsToggledBackground(_selectionStyle.attributes);
     _isWhite = _isToggledColor &&
-        _selectionStyle.attributes["color"].value == '#ffffff';
+        _selectionStyle.attributes["color"]!.value == '#ffffff';
     _isWhitebackground = _isToggledBackground &&
-        _selectionStyle.attributes["background"].value == '#ffffff';
+        _selectionStyle.attributes["background"]!.value == '#ffffff';
     widget.controller.addListener(_didChangeEditingValue);
   }
 
@@ -671,9 +671,9 @@ class _ColorButtonState extends State<ColorButton> {
       _isToggledBackground =
           _getIsToggledBackground(_selectionStyle.attributes);
       _isWhite = _isToggledColor &&
-          _selectionStyle.attributes["color"].value == '#ffffff';
+          _selectionStyle.attributes["color"]!.value == '#ffffff';
       _isWhitebackground = _isToggledBackground &&
-          _selectionStyle.attributes["background"].value == '#ffffff';
+          _selectionStyle.attributes["background"]!.value == '#ffffff';
     }
   }
 
@@ -686,13 +686,13 @@ class _ColorButtonState extends State<ColorButton> {
   @override
   Widget build(BuildContext context) {
     final theme = Theme.of(context);
-    Color iconColor = _isToggledColor && !widget.background && !_isWhite
+    Color? iconColor = _isToggledColor && !widget.background && !_isWhite
-        ? stringToColor(_selectionStyle.attributes["color"].value)
+        ? stringToColor(_selectionStyle.attributes["color"]!.value)
         : theme.iconTheme.color;
 
-    Color iconColorBackground =
+    Color? iconColorBackground =
         _isToggledBackground && widget.background && !_isWhitebackground
-            ? stringToColor(_selectionStyle.attributes["background"].value)
+            ? stringToColor(_selectionStyle.attributes["background"]!.value)
             : theme.iconTheme.color;
 
     Color fillColor = _isToggledColor && !widget.background && _isWhite
@@ -748,10 +748,10 @@ class HistoryButton extends StatefulWidget {
   final QuillController controller;
 
   HistoryButton(
-      {Key key,
+      {Key? key,
-      @required this.icon,
+      required this.icon,
-      @required this.controller,
+      required this.controller,
-      @required this.undo})
+      required this.undo})
       : assert(icon != null),
         assert(controller != null),
         assert(undo != null),
@@ -762,8 +762,8 @@ class HistoryButton extends StatefulWidget {
 }
 
 class _HistoryButtonState extends State<HistoryButton> {
-  Color _iconColor;
+  Color? _iconColor;
-  ThemeData theme;
+  late ThemeData theme;
 
   @override
   Widget build(BuildContext context) {
@@ -823,10 +823,10 @@ class IndentButton extends StatefulWidget {
   final bool isIncrease;
 
   IndentButton(
-      {Key key,
+      {Key? key,
-      @required this.icon,
+      required this.icon,
-      @required this.controller,
+      required this.controller,
-      @required this.isIncrease})
+      required this.isIncrease})
       : assert(icon != null),
         assert(controller != null),
         assert(isIncrease != null),
@@ -880,7 +880,7 @@ class ClearFormatButton extends StatefulWidget {
 
   final QuillController controller;
 
-  ClearFormatButton({Key key, @required this.icon, @required this.controller})
+  ClearFormatButton({Key? key, required this.icon, required this.controller})
       : assert(icon != null),
         assert(controller != null),
         super(key: key);
@@ -913,11 +913,11 @@ class _ClearFormatButtonState extends State<ClearFormatButton> {
 class QuillToolbar extends StatefulWidget implements PreferredSizeWidget {
   final List<Widget> children;
 
-  const QuillToolbar({Key key, @required this.children}) : super(key: key);
+  const QuillToolbar({Key? key, required this.children}) : super(key: key);
 
   factory QuillToolbar.basic(
-      {Key key,
+      {Key? key,
-      @required QuillController controller,
+      required QuillController controller,
       double toolbarIconSize = 18.0,
       bool showBoldButton = true,
       bool showItalicButton = true,
@@ -936,7 +936,7 @@ class QuillToolbar extends StatefulWidget implements PreferredSizeWidget {
       bool showLink = true,
       bool showHistory = true,
       bool showHorizontalRule = false,
-      OnImagePickCallback onImagePickCallback}) {
+      OnImagePickCallback? onImagePickCallback}) {
     iconSize = toolbarIconSize;
     return QuillToolbar(key: key, children: [
       Visibility(
@@ -1155,16 +1155,16 @@ class _QuillToolbarState extends State<QuillToolbar> {
 }
 
 class QuillIconButton extends StatelessWidget {
-  final VoidCallback onPressed;
+  final VoidCallback? onPressed;
-  final Widget icon;
+  final Widget? icon;
   final double size;
-  final Color fillColor;
+  final Color? fillColor;
   final double hoverElevation;
   final double highlightElevation;
 
   const QuillIconButton({
-    Key key,
+    Key? key,
-    @required this.onPressed,
+    required this.onPressed,
     this.icon,
     this.size = 40,
     this.fillColor,
@@ -1193,7 +1193,7 @@ class QuillIconButton extends StatelessWidget {
 
 class QuillDropdownButton<T> extends StatefulWidget {
   final double height;
-  final Color fillColor;
+  final Color? fillColor;
   final double hoverElevation;
   final double highlightElevation;
   final Widget child;
@@ -1202,15 +1202,15 @@ class QuillDropdownButton<T> extends StatefulWidget {
   final ValueChanged<T> onSelected;
 
   const QuillDropdownButton({
-    Key key,
+    Key? key,
     this.height = 40,
     this.fillColor,
     this.hoverElevation = 1,
     this.highlightElevation = 1,
-    @required this.child,
+    required this.child,
-    @required this.initialValue,
+    required this.initialValue,
-    @required this.items,
+    required this.items,
-    @required this.onSelected,
+    required this.onSelected,
   }) : super(key: key);
 
   @override
@@ -1239,7 +1239,7 @@ class _QuillDropdownButtonState<T> extends State<QuillDropdownButton<T>> {
   void _showMenu() {
     final popupMenuTheme = PopupMenuTheme.of(context);
     final button = context.findRenderObject() as RenderBox;
-    final overlay = Overlay.of(context).context.findRenderObject() as RenderBox;
+    final overlay = Overlay.of(context)!.context.findRenderObject() as RenderBox;
     final position = RelativeRect.fromRect(
       Rect.fromPoints(
         button.localToGlobal(Offset.zero, ancestor: overlay),
@@ -1259,7 +1259,7 @@ class _QuillDropdownButtonState<T> extends State<QuillDropdownButton<T>> {
       // widget.shape ?? popupMenuTheme.shape,
       color: popupMenuTheme.color, // widget.color ?? popupMenuTheme.color,
       // captureInheritedThemes: widget.captureInheritedThemes,
-    ).then((T newValue) {
+    ).then((T? newValue) {
       if (!mounted) return null;
       if (newValue == null) {
         // if (widget.onCanceled != null) widget.onCanceled();

pubspec.yaml

@@ -6,7 +6,7 @@ homepage: https://bulletjournal.us/home/index.html
 repository: https://github.com/singerdmx/flutter-quill.git
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
+  sdk: '>=2.12.0 <3.0.0'
   flutter: ">=1.17.0"
 
 dependencies: