@Test void builder_merge_localEndpoint() {
    Span merged = Span.newBuilder()
      .merge(base.toBuilder().localEndpoint(FRONTEND).build()).build();

    assertThat(merged).isEqualToComparingFieldByField(
      base.toBuilder().localEndpoint(FRONTEND).build()
    );
  }
Catches common error when zero is passed instead of null for a timestamp
zipkin/src/test/java/zipkin2/SpanTest.java