@Test
public void toJsonWithEmptyPayloadReturnsExpected() {

    final SendThingMessage<?> underTest =
            SendThingMessage.of(THING_ID, MESSAGE_EMPTY_PAYLOAD, TestConstants.EMPTY_DITTO_HEADERS);
    final JsonObject actualJson = underTest.toJson(FieldType.regularOrSpecial());
    assertThat(actualJson).isEqualTo(KNOWN_JSON_WITH_EMPTY_PAYLOAD);
}