public long reduceKeysToLong(long parallelismThreshold,
                                 ToLongFunction<? super K> transformer,
                                 long basis,
                                 LongBinaryOperator reducer) {
        if (transformer == null || reducer == null)
            throw new NullPointerException();
        return new MapReduceKeysToLongTask<K,V>
            (null, batchFor(parallelismThreshold), 0, 0, table,
             null, transformer, basis, reducer).invoke();
    }
public long reduceKeysToLong(long parallelismThreshold,
                                 ToLongFunction<? super K> transformer,
                                 long basis,
                                 LongBinaryOperator reducer)