@Test void acceptSpans_emptyMessageOk() {
    byte[] bytes = new byte[] {'[', ']'};
    collector.acceptSpans(bytes, callback);

    verify(collector).acceptSpans(bytes, SpanBytesDecoder.JSON_V1, callback);

    verify(callback).onSuccess(null);
    assertThat(getLoggingEvents()).isEmpty();
    assertThat(storage.getTraces()).isEmpty();
  }
Tags in zipkin v2 model are stringly typed.
zipkin-collector/core/src/test/java/zipkin2/collector/CollectorTest.java