Remove comment, simplify null-guard

synapse/handlers/read_marker.py

@@ -40,13 +40,10 @@ class ReadMarkerHandler(BaseHandler):
         the read marker has changed.
         """
 
-        # Get ordering for existing read marker
         with (yield self.read_marker_linearizer.queue((room_id, user_id))):
             account_data = yield self.store.get_account_data_for_room(user_id, room_id)
 
-            existing_read_marker = None
-            if "m.read_marker" in account_data:
-                existing_read_marker = account_data["m.read_marker"]
+            existing_read_marker = account_data.get("m.read_marker", None)
 
             should_update = True