@Test protected void readback_minimalErrorSpan(TestInfo testInfo) throws Exception {
    String testSuffix = testSuffix(testInfo);
    String serviceName = appendSuffix("isao01", testSuffix);
    Span errorSpan = Span.newBuilder().traceId(newTraceId()).id("1")
      .timestamp(TODAY * 1000L)
      .localEndpoint(Endpoint.newBuilder().serviceName(serviceName).build())
      .kind(CLIENT)
      .putTag("error", "")
      .build();
    accept(errorSpan);

    QueryRequest.Builder requestBuilder =
      requestBuilder().serviceName(serviceName); // so this doesn't die on cassandra v1

    assertGetTracesReturns(requestBuilder.build(), List.of(errorSpan));

    assertGetTracesReturns(
      requestBuilder.parseAnnotationQuery("error").build(), List.of(errorSpan));

    assertGetTracesReturnsEmpty(
      requestBuilder.parseAnnotationQuery("error=1").build());

    assertGetTraceReturns(errorSpan);
  }
The following skeletal span is used in dependency linking.

<p>Notably this guards empty tag values work
zipkin-tests/src/main/java/zipkin2/storage/ITSpanStore.java