anchor.diff:  
       _overrideNextRouteGist = null;
   
  +    _gistIdInProgress = gistId;
       gistLoader.loadGist(gistId).then((Gist gist) {
         _editableGist.setBackingGist(gist);
   
  
positive.code:       MDCSwitch(querySelector('#null-safety-switch'));
    final Element? _channelSwitch = querySelector('#channel-switch');
    MDCMenu? _channelsMenu;
  
    late Splitter _rightSplitter;
    bool _rightSplitterConfigured = false;
  
negative.code:       final message = 'Error loading gist $gistId.';
        showSnackbar(message);
        _logger.severe('$message: $e');
      }).whenComplete(() {
        _gistIdInProgress = null;
      });
    }
  
  