anchor.diff:    /// Build a widget to display in the status line.
     ///
     /// If this method returns `null`, then no page specific status is displayed.
  -  Widget buildStatus(BuildContext context, TextTheme textTheme) {
  +  Widget? buildStatus(BuildContext context, TextTheme textTheme) {
       return null;
     }
   }
  
positive.code:   });
  
    const Screen.conditional({
      @required String id,
      String requiresLibrary,
      bool requiresDartVm = false,
      bool requiresDebugBuild = false,
      bool requiresVmDeveloperMode = false,
      bool worksOffline = false,
      bool Function(FlutterVersion currentVersion) shouldShowForFlutterVersion,
      bool showFloatingDebuggerControls = true,
      String title,
      IconData icon,
      Key tabKey,
    }) : this(
            id,
            requiresLibrary: requiresLibrary,
  
negative.code:   ///
    /// If the screen does not have a custom documentation page, this property
    /// should return `null`.
    String? get docPageId => null;
  
    int get badgeCount => 0;
  
  