@Test void whenServerLabelsAreMissing_kindIsUnknownAndLabelsAreCleared() {
    DependencyLinkV2SpanIterator iterator =
        iterator(
            newRecord().values(traceIdHigh, traceId, parentId, spanId, "ca", TYPE_BOOLEAN, "s1"));
    Span span = iterator.next();

    assertThat(span.kind()).isNull();
    assertThat(span.localEndpoint()).isNull();
    assertThat(span.remoteEndpoint()).isNull();
  }
The linker is biased towards server spans, or client spans that know the peer localEndpoint().
zipkin-storage/mysql-v1/src/test/java/zipkin2/storage/mysql/v1/DependencyLinkV2SpanIteratorTest.java