*
   * @param map the backing map for the returned multimap view
   */
  public static <K extends @Nullable Object, V extends @Nullable Object> SetMultimap<K, V> forMap(
      Map<K, V> map) {
    return new MapMultimap<>(map);
  }

  /** @see Multimaps#forMap */
  private static class MapMultimap<K extends @Nullable Object, V extends @Nullable Object>