return new MapMultimap<>(map);
  }

  /**
   * @see Multimaps#forMap
   */
  private static final class MapMultimap<K extends @Nullable Object, V extends @Nullable Object>
      extends AbstractMultimap<K, V> implements SetMultimap<K, V>, Serializable {
    final Map<K, V> map;

    MapMultimap(Map<K, V> map) {
      this.map = checkNotNull(map);
    }

    @Override
    public int size() {