static Component addToPossiblyInternalFrame(final Component c, final Component toAdd) {
  if (toAdd != null) swing {
    RootPaneContainer frame = getPossiblyInternalFrame(c);
    Container cp = frame.getContentPane();
    new JPanel newCP;
    newCP.setLayout(new BorderLayout);
    newCP.add(BorderLayout.CENTER, cp);
    newCP.add(BorderLayout.SOUTH, toAdd);
    frame.setContentPane(newCP);
    revalidate(frame);
  }
  ret c;
}

Began life as a copy of #1001528