anchor.diff:          const SizedBox(height: denseRowSpacing),
           Expanded(
             child:
  -              _screen != null ? _screen.build(context) : _buildSnapshotError(),
  +              _screen != null ? _screen!.build(context) : _buildSnapshotError(),
           ),
         ],
       );
  
positive.code: 
    Widget _buildSnapshotError() {
      return CenteredMessage(
          'Cannot load snapshot for screen \'${widget.args?.screenId}\'');
    }
  
    void reset() {
  
negative.code: class SnapshotArguments {
    SnapshotArguments(this.screenId);
  
    SnapshotArguments.fromArgs(Map<String, String?> args) : this(args['screen']);
  
    final String? screenId;
  }
  