}

      @Override
      public K next() {
        return entryIterator.next().getKey();
      }
    };
  }

  @GwtIncompatible // Spliterator
  Spliterator<K> keySpliterator() {
    return CollectSpliterators.map(
        entrySet().spliterator(),
        Spliterator.ORDERED | Spliterator.DISTINCT | Spliterator.NONNULL | Spliterator.IMMUTABLE,
        Entry::getKey);
  }