public <U> U search(long parallelismThreshold,
                        BiFunction<? super K, ? super V, ? extends U> searchFunction) {
        if (searchFunction == null) throw new NullPointerException();
        return new SearchMappingsTask<K,V,U>
            (null, batchFor(parallelismThreshold), 0, 0, table,
             searchFunction, new AtomicReference<U>()).invoke();
    }
public <U> U search(long parallelismThreshold,
                        BiFunction<? super K, ? super V, ? extends U> searchFunction)