private static void addIsNullButtonSelector(final IBinding bnd,
Container editor, String rId) {
ButtonSelector bs = new ButtonSelector(SWT.CHECK);
bs.setText("is null");
bs.addListener(SWT.Selection, new SWTEventListener() {
public void handleEvent(AbstractUIElement element, Event event) {
Binding b = (Binding) bnd;
boolean readOnly = b.isReadOnly();
b.setReadOnly(!readOnly);