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