public static String toJson(Message message) {
    StringWriter json = new StringWriter();
    try (JsonWriter jsonWriter = JsonWriter.of(json)) {
      write(message, jsonWriter);
    }
    return json.toString();
  }
@Test
  public void inline_wrapper_of_map() {
    TestNullableMap msg = TestNullableMap.newBuilder()
      .setLabel("world")
      .setTranslations(Translations.newBuilder())
      .build();
    assertThat(toJson(msg)).isEqualTo("{\"label\":\"world\",\"translations\":{}}");

    Translations.Builder translationsBuilder = Translations.newBuilder();
    translationsBuilder.getMutableTranslations().put("one", "un");
    translationsBuilder.getMutableTranslations().put("two", "deux");
    msg = TestNullableMap.newBuilder()
      .setLabel("world")
      .setTranslations(translationsBuilder)
      .build();
    assertThat(toJson(msg)).isEqualTo("{\"label\":\"world\",\"translations\":{\"one\":\"un\",\"two\":\"deux\"}}");
  }