@Test public void nextSpan_shouldnt_tag_null_key() {

  consumerRecord = new ConsumerRecord<>(TEST_TOPIC, 0, 1, null, TEST_VALUE);
  kafkaTracing.nextSpan(consumerRecord).start().finish();
  assertThat(spans.get(0).tags())
    .containsOnly(entry("kafka.topic", TEST_TOPIC));
}