public double reduceKeysToDouble(long parallelismThreshold,
                                     ToDoubleFunction<? super K> transformer,
                                     double basis,
                                     DoubleBinaryOperator reducer) {
        if (transformer == null || reducer == null)
            throw new NullPointerException();
        return new MapReduceKeysToDoubleTask<K,V>
            (null, batchFor(parallelismThreshold), 0, 0, table,
             null, transformer, basis, reducer).invoke();
    }
public double reduceKeysToDouble(long parallelismThreshold,
                                     ToDoubleFunction<? super K> transformer,
                                     double basis,
                                     DoubleBinaryOperator reducer)