public List<String> getHiddenWidgetIds() {
   DashboardPanel<T> dashboard = getDashboardPanel();
   List<String> ids = new ArrayList<String>();
   for (AbstractWidget<T> widget : dashboard.getWidgets()) {
     if (widget.isHidden()) ids.add(widget.getId());
   }
   return ids;
 }
 @Override
 public void detachModels() {
   super.detachModels();
   roleModel.detach();
 }