*/
  public static <K extends @Nullable Object, V extends @Nullable Object>
      ListMultimap<K, V> unmodifiableListMultimap(ListMultimap<K, V> delegate) {
    if (delegate instanceof UnmodifiableListMultimap || delegate instanceof ImmutableListMultimap) {
      return delegate;
    }
    return new UnmodifiableListMultimap<>(delegate);
  }

  /**
   * Simply returns its argument.
   *