anchor.diff:  /*
    * RenderObjectWrappers correspond to a desired state of a RenderObject.
    * They are fully immutable, with one exception: A UINode which is a
  - * Component which lives within an OneChildListRenderObjectWrapper's
  + * Component which lives within an MultiChildRenderObjectWrapper's
    * children list, may be replaced with the "old" instance if it has
    * become stateful.
    */
  
positive.code: 
  final List<UINode> _emptyList = new List<UINode>();
  
  abstract class OneChildListRenderObjectWrapper extends RenderObjectWrapper {
  
    // In OneChildListRenderObjectWrapper subclasses, slots are RenderObject nodes
    // to use as the "insert before" sibling in ContainerRenderObjectMixin.add() calls
  
    final List<UINode> children;
  
    OneChildListRenderObjectWrapper({
      Object key,
      List<UINode> children
    }) : this.children = children == null ? _emptyList : children,
  
negative.code:   }
  }
  
  class FlexContainer extends MultiChildRenderObjectWrapper {
    RenderFlex root;
    RenderFlex createNode() => new RenderFlex(direction: this.direction);
  
  