@Override
    public <KR, VR> KStream<KR, VR> map(final KeyValueMapper<? super K, ? super V, ? extends KeyValue<? extends KR, ? extends VR>> mapper) {
        return map(mapper, NamedInternal.empty());
    }
@Test
    public void shouldNotAllowNullMapperOnMap() {
        final NullPointerException exception = assertThrows(
            NullPointerException.class,
            () -> testStream.map(null));
        assertThat(exception.getMessage(), equalTo("mapper can't be null"));
    }