anchor.diff:  
   class ReleaseNotes extends AnimatedWidget {
     const ReleaseNotes({
  -    Key key,
  -    @required this.releaseNotesController,
  -    @required Animation<double> visibilityAnimation,
  -    @required this.markdownData,
  +    Key? key,
  +    required this.releaseNotesController,
  +    required Animation<double> visibilityAnimation,
  +    required this.markdownData,
     }) : super(key: key, listenable: visibilityAnimation);
   
     final ReleaseNotesController releaseNotesController;
   
  -  final String markdownData;
  +  final String? markdownData;
   
     @override
     Widget build(BuildContext context) {
  
positive.code: 
    static const _flutterDocsSite = 'https://docs.flutter.dev';
  
    ValueListenable<String> get releaseNotesMarkdown => _releaseNotesMarkdown;
  
    final _releaseNotesMarkdown = ValueNotifier<String>(null);
  
    ValueListenable<bool> get releaseNotesVisible => _releaseNotesVisible;
  
  
negative.code: 
  class ReleaseNotesViewer extends StatefulWidget {
    const ReleaseNotesViewer({
      Key? key,
      required this.releaseNotesController,
      required this.child,
    }) : super(key: key);
  
    final ReleaseNotesController releaseNotesController;
  