@Test void traceByServiceSpan_indexesLocalServiceNameAndEmptySpanName() {
    Span span = spanWithoutAnnotationsOrTags;

    AggregateCall<?, Void> call = (AggregateCall<?, Void>) consumer.accept(List.of(span));
    assertThat(call.delegate())
      .filteredOn(c -> c instanceof InsertTraceByServiceSpan)
      .extracting("input.service", "input.span")
      .containsExactly(
        tuple(FRONTEND.serviceName(), span.name()), tuple(FRONTEND.serviceName(), ""));
  }
To allow lookups w/o a span name, we index "". "" is used instead of null to avoid creating
tombstones.
zipkin-storage/cassandra/src/test/java/zipkin2/storage/cassandra/CassandraSpanConsumerTest.java