@Test void ipv6_downcases() {
    Endpoint endpoint = Endpoint.newBuilder().ip("2001:DB8::C001").build();

    assertThat(endpoint.ipv6())
      .isEqualTo("2001:db8::c001");
  }
Many getPort operations return -1 by default. Leniently coerse to null.
zipkin/src/test/java/zipkin2/EndpointTest.java