public <U> void forEachKey(long parallelismThreshold,
                               Function<? super K, ? extends U> transformer,
                               Consumer<? super U> action) {
        if (transformer == null || action == null)
            throw new NullPointerException();
        new ForEachTransformedKeyTask<K,V,U>
            (null, batchFor(parallelismThreshold), 0, 0, table,
             transformer, action).invoke();
    }
public <U> void forEachKey(long parallelismThreshold,
                               Function<? super K, ? extends U> transformer,
                               Consumer<? super U> action)