Fixed handling of numeric-only report_request_ids

If a report_request_id (generated by a different implementation) was
completely numeric, it would get turned into an int instead of a str.

This solves that problem, making the resulting report_request_ids always
be strings, which might be important when offloading thing to type-
sensitive code.

openleadr/utils.py

@@ -139,8 +139,11 @@ def normalize_key(key):
                 if not isinstance(d[key]['report_request_id'], list):
                     d[key]['report_request_id'] = [d[key]['report_request_id']]
 
-                d[key] = [{'report_request_id': rrid}
-                          for rrid in d[key]['report_request_id']]
+                # When collecting the report_request_ids, make sure even numeric
+                # ids get turned into strings.
+                d[key] = [{'report_request_id': str(rrid)}
+                          for rrid in d[key]['report_request_id']
+                          if d[key]['report_request_id'] is not None]
 
             # If there are no pending reports, make sure we get an empty list back
             # so any iteration can proceed as normal.

test/test_message_conversion.py

@@ -111,6 +111,8 @@ def create_dummy_event(ven_id):
                                                   {'response_code': 200, 'response_description': 'OK', 'request_id': generate_id(), 'event_id': generate_id(), 'modification_number': 1, 'opt_type': 'optIn'}],
                                  ven_id='123ABC')),
 ('oadrCreatedReport', dict(response={'response_code': 200, 'response_description': 'OK', 'request_id': generate_id()}, pending_reports=[{'report_request_id': generate_id()}], ven_id='123ABC')),
+('oadrCreatedReport', dict(response={'response_code': 200, 'response_description': 'OK', 'request_id': generate_id()}, pending_reports=[], ven_id='123ABC')),
+('oadrCreatedReport', dict(response={'response_code': 200, 'response_description': 'OK', 'request_id': generate_id()}, pending_reports=[{'report_request_id': '123'}], ven_id='123ABC')),
 ('oadrCreatedReport', dict(response={'response_code': 200, 'response_description': 'OK', 'request_id': generate_id()}, pending_reports=[{'report_request_id': generate_id()}, {'report_request_id': generate_id()}], ven_id='123ABC')),
 ('oadrCreatedEvent', dict(response={'response_code': 200, 'response_description': 'OK', 'request_id': None},
                                  event_responses=[{'response_code': 200, 'response_description': 'OK', 'request_id': generate_id(),