Web.get_or_create bug fix: handle opted out users

fixes https://console.cloud.google.com/errors/detail/CJ2U0_Hq6cHnUA;time=P30D?project=bridgy-federated

tests/test_web.py

@@ -495,6 +495,17 @@ class WebTest(TestCase):
         self.assert_entities_equal(user, Web.get_by_id('foo.bar'))
         self.assertIsNone(Web.get_by_id('..foo.bar.'))
 
+    def test_get_or_create_existing(self, *_):
+        user = Web.get_or_create('user.com')
+        self.assertEqual('user.com', user.key.id())
+        self.assert_entities_equal(user, self.user)
+
+    def test_get_or_create_existing_opted_out(self, *_):
+        self.user.obj.mf2['properties']['summary'] = '#nobridge'
+        self.user.obj.put()
+        self.user.put()
+        self.assertIsNone(Web.get_or_create('user.com'))
+
     def test_bad_source_url(self, *mocks):
         orig_count = Object.query().count()
 

web.py

@@ -94,7 +94,11 @@ class Web(User, Protocol):
         Normalizing currently consists of lower casing and removing leading and
         trailing dots.
         """
-        domain = cls.key_for(id).id().lower().strip('.')
+        key = cls.key_for(id)
+        if not key:
+            return None  # opted out
+
+        domain = key.id().lower().strip('.')
         return super().get_or_create(domain, **kwargs)
 
     @ndb.ComputedProperty