anchor.diff:  ///   @override
   ///   void didChangeDependencies() {
   ///     super.didChangeDependencies();
  -///     routeObserver.subscribe(this, ModalRoute.of(context));
  +///     routeObserver.subscribe(this, ModalRoute.of(context)!);
   ///   }
   ///
   ///   @override
  
positive.code: ///
  /// ```dart
  /// // Register the RouteObserver as a navigation observer.
  /// final RouteObserver<PageRoute> routeObserver = RouteObserver<PageRoute>();
  /// void main() {
  ///   runApp(MaterialApp(
  ///     home: Container(),
  
negative.code: /// be given with their type arguments. Since the [Route] class and its
  /// subclasses have a type argument, this includes the arguments passed to this
  /// class. Consider using `dynamic` to specify the entire class of routes rather
  /// than only specific subtypes. For example, to watch for all [ModalRoute]
  /// variants, the `RouteObserver<ModalRoute<dynamic>>` type may be used.
  ///
  /// {@tool snippet}
  ///
  