: collection.iterator();
  }

  /** Set decorator that stays in sync with the multimap values for a key. */
  @WeakOuter
  final class WrappedSet extends WrappedCollection implements Set<V> {
    WrappedSet(@ParametricNullness K key, Set<V> delegate) {
      super(key, delegate, null);
    }

    @Override
    public boolean removeAll(Collection<?> c) {
      if (c.isEmpty()) {