@Test
public void tryToGetInstanceWithNullStatusCode() {

    assertThatNullPointerException()
            .isThrownBy(
                    () -> ImmutableAcknowledgement.of(KNOWN_ACK_LABEL, KNOWN_ENTITY_ID, null, dittoHeaders, null))
            .withMessage("The statusCode must not be null!")
            .withNoCause();
}