anchor.diff:    @visibleForTesting
     void notifyListeners() {
       super.notifyListeners();
  -
       if (_ignorableListeners != null) {
         final List<VoidCallback> localListeners =
             List<VoidCallback>.from(_ignorableListeners);
  
positive.code:               exception: exception,
                stack: stack,
                library: 'Photoview library',
                context: ErrorDescription(
                    'while dispatching notifications for $runtimeType'),
                informationCollector: () sync* {
                  yield DiagnosticsProperty<IgnorableChangeNotifier>(
                      '$runtimeType sending notification', this);
                },
              ),
            );
          }
  
negative.code:   bool _debugAssertNotDisposed() {
      assert(() {
        if (_ignorableListeners == null) {
          AssertionError(['A $runtimeType was used after being disposed.', 'Once you have called dispose() on a $runtimeType, it can no longer be used.']);
        }
        return true;
      }());
  