if (path == null)
if (path == null || isExpanded(path))
  public void expandPath(TreePath path)  {    // Don't expand if path is null    if (path == null)      return;    try      {        fireTreeWillExpand(path);      }    catch (ExpandVetoException ev)      {        // We do nothing if attempt has been vetoed.      }    setExpandedState(path, true);    fireTreeExpanded(path);  }