V output(@ParametricNullness K key, @ParametricNullness V value) {
        return value;
      }
    };
  }

  @Override
  Spliterator<V> valueSpliterator() {
    return CollectSpliterators.flatMap(
        map.values().spliterator(), Collection::spliterator, Spliterator.SIZED, size());
  }

  /*
   * TODO(kevinb): should we copy this javadoc to each concrete class, so that

```
scala> val file = sc.textFile("s3a://testbucket/testdata")
file: org.apache.spark.rdd.RDD[String] = s3a://testbucket/testdata MapPartitionsRDD[1] at textFile at <console>:24

scala> val counts = file.flatMap(line => line.split(" ")).map(word => (word, 1)).reduceByKey(_ + _)
counts: org.apache.spark.rdd.RDD[(String, Int)] = ShuffledRDD[4] at reduceByKey at <console>:25

scala> counts.saveAsTextFile("s3a://testbucket/wordcount")

         */
        return immutableEntry(requireNonNull(currentKey), valueItr.next());
      }
    };
  }

  @Override
  Spliterator<Entry<K, V>> entrySpliterator() {
    return CollectSpliterators.flatMap(
        asMap().entrySet().spliterator(),
        keyToValueCollectionEntry -> {
          K key = keyToValueCollectionEntry.getKey();
          Collection<V> valueCollection = keyToValueCollectionEntry.getValue();

        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(
                rowEntry.getValue().entrySet().spliterator(),

                                HashMap::putAll));
            }
            propMap.put(DEFAULT_LABEL_VALUES, map);
        }
        return map.entrySet().stream().flatMap(e -> {
            final String key = e.getKey();
            if (StringUtil.isEmpty(key) || userBean