@Nullable
  @Override
  protected JComponent createCenterPanel() {
    ToolbarDecorator decorator = ToolbarDecorator.createDecorator(myTree).
      addExtraAction(new SelectAllButton()).
      addExtraAction(new UnselectAllButton()).
      addExtraAction(new ShowSelectedOnlyButton()).
      addExtraAction(new SelectRequiredButton()).
      setToolbarPosition(ActionToolbarPosition.BOTTOM);

    contentPanel.add(decorator.createPanel());
    loadingPanel = new JBLoadingPanel(new BorderLayout(), getDisposable());
    loadingPanel.add(mainPanel, BorderLayout.CENTER);
    return loadingPanel;
  }
@Nullable
  @Override
  protected JComponent createCenterPanel()