* @param <OutElementT> the element type of the output spliterators
   */
  static final class FlatMapSpliteratorOfObject<
          InElementT extends @Nullable Object, OutElementT extends @Nullable Object>
      extends FlatMapSpliterator<InElementT, OutElementT, Spliterator<OutElementT>> {
    FlatMapSpliteratorOfObject(
        @Nullable Spliterator<OutElementT> prefix,
        Spliterator<InElementT> from,