Merge pull request #452 from juju/johnsca/NoneType-results

#452

Apparently, `list_offers` can return a result with a None value instead of an empty list (or no response key), leading to an error like the following:

```python-traceback
Traceback (most recent call last):
 File "/home/johnsca/juju/projects/kubernetes-jenkins/jobs/integration/conftest.py", line 233, in k8s_model
 offers = [offer.offer_name for offer in (await k8s_model.list_offers()).results]
 File "/home/johnsca/juju/projects/kubernetes-jenkins/.tox/py3/lib/python3.8/site-packages/juju/model.py", line 1989, in list_offers
 return await controller.list_offers(self.info.name)
 File "/home/johnsca/juju/projects/kubernetes-jenkins/.tox/py3/lib/python3.8/site-packages/juju/controller.py", line 769, in list_offers
 return await facade.ListApplicationOffers(filters=[params])
 File "/home/johnsca/juju/projects/kubernetes-jenkins/.tox/py3/lib/python3.8/site-packages/juju/client/facade.py", line 480, in wrapper
 reply = await f(*args, **kwargs)
 File "/home/johnsca/juju/projects/kubernetes-jenkins/.tox/py3/lib/python3.8/site-packages/juju/client/_client2.py", line 2413, in ListApplicationOffers
 reply = await self.rpc(msg)
 File "/home/johnsca/juju/projects/kubernetes-jenkins/.tox/py3/lib/python3.8/site-packages/juju/client/facade.py", line 623, in rpc
 result = await self.connection.rpc(msg, encoder=TypeEncoder)
 File "/home/johnsca/juju/projects/kubernetes-jenkins/.tox/py3/lib/python3.8/site-packages/juju/client/connection.py", line 484, in rpc
 for res in result['response']['results']:
TypeError: 'NoneType' object is not iterable
```

Author: jujubot

juju/client/connection.py

@@ -482,7 +482,7 @@ async def rpc(self, msg, encoder=None):
             # errors, or perhaps a keyword parameter to the rpc method
             # could be added to trigger this behaviour.
             err_results = []
-            for res in result['response']['results']:
+            for res in result['response']['results'] or []:
                 if res.get('error', {}).get('message'):
                     err_results.append(res['error']['message'])
             if err_results:

tests/unit/test_connection.py

@@ -165,3 +165,33 @@ async def test_follow_redirect(event_loop):
         if con:
             assert con.connect_params()['endpoint'] == "42.42.42.42:4242"
             await con.close()
+
+
+@pytest.mark.asyncio
+async def test_rpc_none_results(event_loop):
+    ws = WebsocketMock([
+        {'request-id': 1, 'response': {'results': None}},
+    ])
+    expected_responses = [
+        {'request-id': 1, 'response': {'results': None}},
+    ]
+    minimal_facades = [{'name': 'Pinger', 'versions': [1]}]
+    con = None
+    try:
+        with \
+                mock.patch('websockets.connect', base.AsyncMock(return_value=ws)), \
+                mock.patch(
+                    'juju.client.connection.Connection.login',
+                    base.AsyncMock(return_value={'response': {
+                        'facades': minimal_facades,
+                    }}),
+                ), \
+                mock.patch('juju.client.connection.Connection._get_ssl'), \
+                mock.patch('juju.client.connection.Connection._pinger', base.AsyncMock()):
+            con = await Connection.connect('0.1.2.3:999')
+        actual_responses = []
+        actual_responses.append(await con.rpc({'version': 1}))
+        assert actual_responses == expected_responses
+    finally:
+        if con:
+            await con.close()