@SuppressWarnings("unchecked")
 private static <T> Collection<T> unmodifiableComposite(
     final Collection<T> coll1, final Collection<T> coll2) {
   final CompositeCollection compColl = new CompositeCollection();
   compColl.addComposited(coll1, coll2);
   return Collections.unmodifiableCollection(compColl);
 }