docs: Collection<V> wrapCollection(@Nullable K key, Collection<V> collection) {
      // We don't deal with NavigableSet here yet for GWT reasons -- instead,
      // non-GWT TreeMultimap explicitly overrides this and uses NavigableSet.
      if (collection instanceof SortedSet) {
        return new WrappedSortedSet(key, (SortedSet<V>) collection, null);
      } else if (collection instanceof Set) {
        return new WrappedSet(key, (Set<V>) collection);
      } else if (collection instanceof List) {
        return wrapList(key, (List<V>) collection, null);
      } else {
        return new WrappedCollection(key, collection, null);
      }
    }