@Test
public void tryToAcceptNullValue() {

    final DittoHeaderDefinition headerDefinition = DittoHeaderDefinition.AUTHORIZATION_CONTEXT;
    final JsonObjectValueValidator underTest = JsonObjectValueValidator.getInstance();
    assertThatExceptionOfType(DittoHeaderInvalidException.class)
            .isThrownBy(() -> underTest.accept(headerDefinition, null))
            .withMessageContaining("null")
            .withMessageContaining(headerDefinition.getKey())
            .withMessageEndingWith("is not a valid JsonObject.")
            .withNoCause();
}