* @param <OutConsumerT> the specialized consumer type for the primitive output type
   * @param <OutSpliteratorT> the primitive spliterator type associated with {@code OutElementT}
   */
  abstract static class FlatMapSpliteratorOfPrimitive<
          InElementT extends @Nullable Object,
          OutElementT extends @Nullable Object,
          OutConsumerT,
          OutSpliteratorT extends