@Test void span_read_kind_tolerant() {
    assertRoundTrip(spanBuilder().kind(Span.Kind.CONSUMER).build());

    bytes[23] = (byte) (Span.Kind.values().length + 1); // undefined kind
    assertThat(SPAN.read(ReadBuffer.wrap(bytes)))
      .isEqualTo(spanBuilder().build()); // skips undefined kind instead of dying

    bytes[23] = 0; // serialized zero
    assertThat(SPAN.read(ReadBuffer.wrap(bytes)))
      .isEqualTo(spanBuilder().build());
  }
A map entry is an embedded messages: one for field the key and one for the value
zipkin/src/test/java/zipkin2/internal/Proto3ZipkinFieldsTest.java