private void addToPanel(JPanel panel, GridBagConstraints gc) {
    builders.stream().filter(b -> b.constrainsValid()).forEach(b -> b.addToPanel(panel, gc, splitColumns));

    if (!expand) {
      gc.gridx = 0;
      gc.anchor = GridBagConstraints.PAGE_END;
      gc.fill = GridBagConstraints.BOTH;
      gc.weighty = 1.0;
      gc.insets = JBUI.insets(0);
      gc.gridwidth = gridWidth();
      panel.add(new JPanel(), gc);
    }
  }
private void addToPanel(JPanel panel, GridBagConstraints gc)