anchor.diff:    final Duration duration;
   
     @override
  -  AnimatedWidgetBaseState<ImplicitlyAnimatedWidget> createState();
  +  ImplicitlyAnimatedWidgetState<ImplicitlyAnimatedWidget> createState();
   
     @override
     void debugFillProperties(DiagnosticPropertiesBuilder properties) {
  
positive.code: 
  /// A base class for widgets with implicit animations.
  ///
  /// Subclasses must implement the [forEachTween] method to help
  /// [AnimatedWidgetBaseState] iterate through the subclasses' widget's fields
  /// and animate them.
  abstract class AnimatedWidgetBaseState<T extends ImplicitlyAnimatedWidget> extends State<T> with SingleTickerProviderStateMixin {
    AnimationController _controller;
  
    /// The animation driving this widget's implicit animations.
  
negative.code:       duration: widget.duration,
        debugLabel: '${widget.toStringShort()}',
        vsync: this,
      );
      _updateCurve();
      _constructTweens();
    }
  