static <A> L<A> getComboBoxItems(JComboBox<A> cb) {
  ret cb == null ?: swing(-> {
    ComboBoxModel<A> model = cb.getModel();
    int n = model.getSize();
    L<A> l = emptyList(n);
    for i to n:
      l.add(model.getElementAt(i));
    ret l;
  });
}