MetalLookAndFeelのJInternalFrameタイトルバーでBumpsを非表示にする

JInternalFrame f1 = new JInternalFrame("basic", true, true, true, true) {
  @Override public void updateUI() {
    super.updateUI();
    setUI(new BasicInternalFrameUI(this) {
      @Override protected JComponent createNorthPane(JInternalFrame w) {
        return new BumpsFreeInternalFrameTitlePane(w);
      }
    });
  }
};
//...
class BumpsFreeInternalFrameTitlePane extends BasicInternalFrameTitlePane {
  protected BumpsFreeInternalFrameTitlePane(JInternalFrame w) {
    super(w);
    setBorder(BorderFactory.createMatteBorder(
        0, 0, 1, 0, MetalLookAndFeel.getPrimaryControlDarkShadow()));
  }
  @Override public Dimension getPreferredSize() {
    Dimension d = super.getPreferredSize();
    d.height = 24;
    return d;
  }
  @Override public void createButtons() {
    super.createButtons();
    Arrays.asList(closeButton, maxButton, iconButton).forEach(b -> {
      b.setContentAreaFilled(false);
      b.setBorder(BorderFactory.createEmptyBorder(2, 5, 2, 5));
    });
  }
}