}
  }

  @Override
  Collection<V> wrapCollection(@ParametricNullness K key, Collection<V> collection) {
    if (collection instanceof NavigableSet) {
      return new WrappedNavigableSet(key, (NavigableSet<V>) collection, null);
    } else {
      return new WrappedSortedSet(key, (SortedSet<V>) collection, null);
    }
  }

  // Following Javadoc copied from Multimap and SortedSetMultimap.