Fix Container insert

lib/models/documents/document.dart

@@ -32,7 +32,8 @@ class Document {
 
   Stream<Tuple3> get changes => _observer.stream;
 
-  Document() : _delta = Delta()..insert('\n') {
+  Document() : _delta = Delta()
+    ..insert('\n') {
     _loadDocument(_delta);
   }
 
@@ -138,7 +139,11 @@ class Document {
         offset += op.length;
       }
     }
+    try {
       _delta = _delta.compose(delta);
+    } catch (e) {
+      throw ('_delta compose failed');
+    }
 
     if (_delta != _root.toDelta()) {
       throw ('Compose failed');
@@ -179,7 +184,8 @@ class Document {
         _root.insert(offset, data, style);
       } else {
         throw ArgumentError.value(doc,
-            'Document Delta can only contain insert operations but ${op.key} found.');
+            'Document Delta can only contain insert operations but ${op
+                .key} found.');
       }
       offset += op.length;
     }

lib/models/documents/nodes/container.dart

@@ -84,6 +84,7 @@ abstract class Container<T extends Node> extends Node {
     if (isNotEmpty) {
       ChildQuery child = queryChild(index, false);
       child.node.insert(child.offset, data, style);
+      return;
     }
 
     // empty