@Nullable
  Tool getSingleSelectedTool() {
    final TreePath[] selectionPaths = myTree.getSelectionPaths();
    if (selectionPaths == null || selectionPaths.length != 1) {
      return null;
    }
    Object toolOrToolGroup = ((CheckedTreeNode)selectionPaths[0].getLastPathComponent()).getUserObject();
    if (toolOrToolGroup instanceof Tool) {
      return (Tool)toolOrToolGroup;
    }
    return null;
  }
@Nullable
  Tool getSingleSelectedTool()