register: Not all clients send a User-Agent header.

In 1fce1c3c73, we added logic to parse
the User-Agent in /register requests; this logic crashed if an HTTP request
was missing that header.

Includes a test for `/register` with no user agent passed; this should catch
similar regressions in the future.

Co-authored-by: Mateusz Mandera <mateusz.mandera@zulip.com>

zerver/lib/compatibility.py

@@ -140,7 +140,7 @@ def is_unsupported_browser(user_agent: str) -> Tuple[bool, Optional[str]]:
     return (False, browser_name)
 
 
-def is_pronouns_field_type_supported(user_agent_str: str) -> bool:
+def is_pronouns_field_type_supported(user_agent_str: Optional[str]) -> bool:
     # In order to avoid users having a bad experience with these
     # custom profile fields disappearing after applying migration
     # 0421_migrate_pronouns_custom_profile_fields, we provide this
@@ -150,6 +150,9 @@ def is_pronouns_field_type_supported(user_agent_str: str) -> bool:
     # TODO/compatibility(7.0): Because this is a relatively minor
     # detail, we can remove this compatibility hack once most users
     # have upgraded to a sufficiently new mobile client.
+    if user_agent_str is None:
+        return True
+
     user_agent = parse_user_agent(user_agent_str)
     if user_agent["name"] != "ZulipMobile":
         return True

zerver/tests/test_event_system.py

@@ -50,6 +50,10 @@ from zerver.views.events_register import (
 
 
 class EventsEndpointTest(ZulipTestCase):
+    def test_events_register_without_user_agent(self) -> None:
+        result = self.client_post("/json/register", skip_user_agent=True)
+        self.assert_json_success(result)
+
     def test_events_register_endpoint(self) -> None:
 
         # This test is intended to get minimal coverage on the

zerver/views/events_register.py

@@ -124,7 +124,9 @@ def events_register_backend(
     client = RequestNotes.get_notes(request).client
     assert client is not None
 
-    pronouns_field_type_supported = is_pronouns_field_type_supported(request.headers["User-Agent"])
+    pronouns_field_type_supported = is_pronouns_field_type_supported(
+        request.headers.get("User-Agent")
+    )
     ret = do_events_register(
         user_profile,
         realm,