return (result == null) ? values = createValues() : result;
  }

  Collection<V> createValues() {
    return new Values();
  }

  Iterator<V> valuesIterator() {
    return new TransformedIterator<Cell<R, C, V>, V>(cellSet().iterator()) {
      @Override
      @ParametricNullness
      V transform(Cell<R, C, V> cell) {
        return cell.getValue();
      }
    };
  }

@GwtCompatible
public final class Maps {
  private Maps() {}

  static <K extends @Nullable Object, V extends @Nullable Object> Iterator<K> keyIterator(
      Iterator<Entry<K, V>> entryIterator) {
    return new TransformedIterator<Entry<K, V>, K>(entryIterator) {
      @Override
      @ParametricNullness
      K transform(Entry<K, V> entry) {
        return entry.getKey();
      }
    };
  }