anchor.diff:    _FilterDialogState<T> createState() => _FilterDialogState<T>();
   }
   
  -class _FilterDialogState<T> extends State<FilterDialog> with AutoDisposeMixin {
  -  TextEditingController queryTextFieldController;
  +class _FilterDialogState<T>
  +    extends State<FilterDialog<FilterControllerMixin, T>>
  +    with AutoDisposeMixin {
  +  late final TextEditingController queryTextFieldController;
   
     @override
     void initState() {
  
positive.code: 
    Widget _buildQueryInstructions() {
      return Text(
        widget.queryInstructions,
        style: Theme.of(context).subtleTextStyle,
      );
    }
  
    void _resetFilters() {
      queryTextFieldController.clear();
      for (final toggleFilter in widget.toggleFilters) {
        toggleFilter.enabled.value = toggleFilter.enabledByDefault;
      }
    }
  }
  
  class ToggleFilterElement extends StatelessWidget {
    const ToggleFilterElement({Key key, @required this.filter}) : super(key: key);
  
    final ToggleFilter filter;
  
  
negative.code:               const SizedBox(height: defaultSpacing),
              ],
              if (widget.toggleFilters != null)
                for (final toggleFilter in widget.toggleFilters!) ...[
                  ToggleFilterElement(filter: toggleFilter),
                ],
            ],
  