@Override
  final UnmodifiableIterator<Cell<R, C, V>> cellIterator() {
    throw new AssertionError("should never be called");
  }

  @Override
  final Spliterator<Cell<R, C, V>> cellSpliterator() {
    throw new AssertionError("should never be called");
  }

  @Override
  public ImmutableCollection<V> values() {
    return (ImmutableCollection<V>) super.values();
  }

  @Override

      @Override
      protected Cell<R, C, @Nullable V> get(int index) {
        return getCell(index);
      }
    };
  }

  @Override
  Spliterator<Cell<R, C, @Nullable V>> cellSpliterator() {
    return CollectSpliterators.<Cell<R, C, @Nullable V>>indexed(
        size(), Spliterator.ORDERED | Spliterator.NONNULL | Spliterator.DISTINCT, this::getCell);
  }

       */
      if (requireNonNull(rowEntry).getValue().isEmpty()) {
        rowIterator.remove();
        rowEntry = null;
      }
    }
  }

  @Override
  Spliterator<Cell<R, C, V>> cellSpliterator() {
    return CollectSpliterators.flatMap(
        backingMap.entrySet().spliterator(),
        (Entry<R, Map<C, V>> rowEntry) ->
            CollectSpliterators.map(