Method name is inconsistent with the method behavior

[epeartree]

Calling method getMessageKeyOrNull() from class ResourceModifiedMessage and ResourceDeliveryMessage will return a value (payloadId) although method setMessageKey() was never called on the object.

How to reproduce:

@Test
void test_getMessageKeyOrNull_whenSetMessageKeyIsNotInvoked_willReturnNull(){
		IBaseResource patient = buildPatient();
		ResourceModifiedMessage payload = new ResourceModifiedMessage(ourFhirContext, patient, 
                BaseResourceMessage.OperationTypeEnum.CREATE);
		assertNull(payload.getMessageKeyOrNull());                 // this fails.

}