anchor.diff:  
   class ReleaseNotesViewer extends StatefulWidget {
     const ReleaseNotesViewer({
  -    Key key,
  -    @required this.releaseNotesController,
  -    @required this.child,
  +    Key? key,
  +    required this.releaseNotesController,
  +    required this.child,
     }) : super(key: key);
   
     final ReleaseNotesController releaseNotesController;
  
positive.code:   static const viewerWidth = 600.0;
  
    /// Animation controller for animating the opening and closing of the viewer.
    AnimationController visibilityController;
  
    /// A curved animation that matches [visibilityController].
    Animation<double> visibilityAnimation;
  
    String markdownData;
  
    bool isVisible;
  
    @override
    void initState() {
  
negative.code: 
  class ReleaseNotes extends AnimatedWidget {
    const ReleaseNotes({
      Key? key,
      required this.releaseNotesController,
      required Animation<double> visibilityAnimation,
      required this.markdownData,
    }) : super(key: key, listenable: visibilityAnimation);
  
    final ReleaseNotesController releaseNotesController;
  
    final String? markdownData;
  
    @override
    Widget build(BuildContext context) {
  