@Test
public void testCompareWhenServiceReferencesAreNull() {

	PropertyServiceReferenceComparator<Object>
		propertyServiceReferenceComparator =
			new PropertyServiceReferenceComparator<>("ranking");
	ServiceReference<Object> serviceReference1 = new TestServiceReference<>(
		"ranking", 1);
	Assert.assertEquals(
		0, propertyServiceReferenceComparator.compare(null, null));
	int compare = propertyServiceReferenceComparator.compare(
		serviceReference1, null);
	Assert.assertTrue(compare < 0);
	Assert.assertEquals(
		propertyServiceReferenceComparator.compare(serviceReference1, null),
		-propertyServiceReferenceComparator.compare(
			null, serviceReference1));
}