User.handle_as: handle when handle isn't set

for https://console.cloud.google.com/errors/detail/CIT9-r3d-MKW5AE;time=P30D?project=bridgy-federated

models.py

@@ -324,6 +324,8 @@ class User(StringIdModel, metaclass=ProtocolUserMeta):
 
         # override web users to always use domain instead of custom username
         handle = self.key.id() if self.LABEL == 'web' else self.handle
+        if not handle:
+            return None
 
         return ids.translate_handle(handle=handle, from_proto=self.__class__,
                                     to_proto=to_proto)

tests/test_models.py

@@ -166,6 +166,15 @@ class UserTest(TestCase):
         self.assertEqual('alice', self.user.username())
         self.assertEqual('@y.z@web.brid.gy', self.user.handle_as('ap'))
 
+    def test_handle_as_None(self):
+        class NoHandle(Fake):
+            @ndb.ComputedProperty
+            def handle(self):
+                return None
+
+        user = NoHandle()
+        self.assertIsNone(user.handle_as(OtherFake))
+
     @patch('requests.get', return_value=requests_response(DID_DOC))
     def test_ap_actor(self, mock_get):
         user = self.make_user('did:plc:abc', cls=ATProto)