return null;
      } else if (unfiltered instanceof SetMultimap) {
        return Collections.unmodifiableSet(Sets.newLinkedHashSet(result));
      } else {
        return Collections.unmodifiableList(result);
      }
    }

    @Override
    Set<K> createKeySet() {
      @WeakOuter
      class KeySetImpl extends Maps.KeySet<K, Collection<V>> {
        KeySetImpl() {