anchor.diff:    // Map from node UID to info.
     Map<String, TreeViewRow> _rowsMap;
     // Saved expanded state of the nodes when reloading the content of the tree.
  -  HashSet<String> _expandedState;
  +  Set<String> _expandedState;
     // When dragging over a cell the tree view, it's the highlighted cell.
     TreeViewCell _currentDragOverCell;
     // Whether the user can drag a cell.
  
positive.code:   }
  
    List<String> get expandedState {
      List<String> result = [];
      if (_rows != null) {
        // Save expanded state.
        _rows.forEach((TreeViewRow row) {
          if (row.expanded) {
            result.add(row.nodeUID);
          }
        });
      }
      return result;
    }
  
    void restoreExpandedState(List<String> expandedState) {
      // Save expanded state.
      _expandedState = new HashSet();
      _expandedState.addAll(expandedState);
  
      _fillRows();
      _expandedState.clear();
      _listView.reloadData();
  
negative.code:     _listView.selection = [];
  
      // Save expanded state.
      _expandedState = new Set();
      if (_rows != null) {
        _expandedState = new Set.from(expandedState);
      }
  
      _fillRows();
  