this.index = index;
    }

    abstract S createSplit(F from, long i);

    @Override
    public @Nullable S trySplit() {
      Spliterator<?> splitOrNull = fromSpliterator.trySplit();
      if (splitOrNull == null) {
        return null;
      }
      @SuppressWarnings("unchecked")
      F split = (F) splitOrNull;
      S result = createSplit(split, index);
      this.index += split.getExactSizeIfKnown();