Initial fix for flip checkbox

lib/models/documents/nodes/node.dart

@@ -44,7 +44,7 @@ abstract class Node extends LinkedListEntry<Node> {
   int getOffset() {
     int offset = 0;
 
-    if (isFirst) {
+    if (list == null || isFirst) {
       return offset;
     }
 

lib/widgets/controller.dart

@@ -64,10 +64,6 @@ class QuillController extends ChangeNotifier {
     }
   }
 
-  void notifyChangeListeners() {
-    notifyListeners();
-  }
-
   void redo() {
     Tuple2 tup = document.redo();
     if (tup.item1) {

lib/widgets/editor.dart

@@ -379,14 +379,12 @@ class _QuillEditorSelectionGestureDetectorBuilder
     }
     // segmentResult.offset == 0 means tap at the beginning of the TextLine
     String listVal = line.style.attributes[Attribute.list.key].value;
+    // TODO: check getEditor().widget.controller.selection
+    // Maybe use formatText instead
     if (listVal == Attribute.unchecked.value) {
-      line.style.attributes
-          .update(Attribute.list.key, (value) => Attribute.checked);
-      getEditor().widget.controller.notifyChangeListeners();
+      getEditor().widget.controller.formatSelection(Attribute.checked);
     } else if (listVal == Attribute.checked.value) {
-      line.style.attributes
-          .update(Attribute.list.key, (value) => Attribute.unchecked);
-      getEditor().widget.controller.notifyChangeListeners();
+      getEditor().widget.controller.formatSelection(Attribute.unchecked);
     }
     return true;
   }