static JInternalFrame getInternalFrame(fO _o) {
  ret _o == null ? null : swing(func -> JInternalFrame {
    O o = _o;
    if (o instanceof ButtonGroup) o = first(buttonsInGroup((ButtonGroup) o));
    if (!(o instanceof Component)) null;
    Component c = (Component) o;
    while (c != null) {
      if (c instanceof JInternalFrame) return (JInternalFrame) c;
      c = c.getParent();
    }
    null;
  });
}

Began life as a copy of #1001428