@Override
  public byte[] serialize(final String topic, final List<?> values) {
    if (values == null) {
      return null;
    }

    final T single = extractOnlyColumn(values, topic);
    return inner.serialize(topic, single);
  }
@Test
  public void shouldSerializeOldStyleNulls() {
    // When:
    final byte[] result = serializer.serialize(TOPIC, null);

    // Then:
    assertThat(result, is(nullValue()));
  }