@Test void builder_clear() {
    assertThat(oneOfEach.toBuilder().clear().traceId("a").id("a").build())
      .isEqualToComparingFieldByField(Span.newBuilder().traceId("a").id("a").build());
  }
Catches common error when zero is passed instead of null for a timestamp
zipkin/src/test/java/zipkin2/SpanTest.java