anchor.diff:        final message = 'Error loading gist $gistId.';
         showSnackbar(message);
         _logger.severe('$message: $e');
  +    }).whenComplete(() {
  +      _gistIdInProgress = null;
       });
     }
   
  
positive.code:       MDCSwitch(querySelector('#null-safety-switch'));
    final Element? _channelSwitch = querySelector('#channel-switch');
    MDCMenu? _channelsMenu;
  
    late Splitter _rightSplitter;
    bool _rightSplitterConfigured = false;
  
negative.code:   }
  
    void _showGist(String gistId) {
      if (_gistIdInProgress == gistId) {
        return;
      }
      // Don't auto-run if we're re-loading some unsaved edits; the gist might
      // have halting issues (#384).
      var loadedFromSaved = false;
  