double (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(); }