@Override
    public <VR> KStream<K, VR> mapValues(final ValueMapper<? super V, ? extends VR> valueMapper) {
        return mapValues(withKey(valueMapper));
    }
@Test
    public void shouldNotAllowNullMapperOnMapValuesWithKeyWithNamed() {
        final NullPointerException exception = assertThrows(
            NullPointerException.class,
            () -> testStream.mapValues(
                (ValueMapperWithKey<Object, Object, Object>) null,
                Named.as("valueMapperWithKey")));
        assertThat(exception.getMessage(), equalTo("valueMapperWithKey can't be null"));
    }