* iterator supports it.
   *
   * <p><b>{@code Stream} equivalent:</b> to concatenate an arbitrary number of streams, use {@code
   * Stream.of(stream1, stream2, ...).flatMap(s -> s)}. If the sources are iterables, use {@code
   * Stream.of(iter1, iter2, ...).flatMap(Streams::stream)}.
   *
   * @throws NullPointerException if any of the provided iterables is {@code null}
   * @since 20.0
   */
  @SafeVarargs

      V output(@ParametricNullness K key, @ParametricNullness V value) {
        return value;
      }
    };
  }

  @Override
  Spliterator<V> valueSpliterator() {
    return CollectSpliterators.flatMap(
        map.values().spliterator(), Collection::spliterator, Spliterator.SIZED, size());
  }

  /*
   * TODO(kevinb): should we copy this javadoc to each concrete class, so that