Sliding sync: omit bump stamp when it is unchanged (#17788)

This saves some DB lookups in rooms

1 files changed, 3 insertions, 1 deletions

diff --git a/synapse/rest/client/sync.py b/synapse/rest/client/sync.py

index 364cf40153..122708e933 100644
--- a/synapse/rest/client/sync.py
+++ b/synapse/rest/client/sync.py
@@ -1010,11 +1010,13 @@ class SlidingSyncRestServlet(RestServlet):
         serialized_rooms: Dict[str, JsonDict] = {}
         for room_id, room_result in rooms.items():
             serialized_rooms[room_id] = {
-                "bump_stamp": room_result.bump_stamp,
                 "notification_count": room_result.notification_count,
                 "highlight_count": room_result.highlight_count,
             }
 
+            if room_result.bump_stamp is not None:
+                serialized_rooms[room_id]["bump_stamp"] = room_result.bump_stamp
+
             if room_result.joined_count is not None:
                 serialized_rooms[room_id]["joined_count"] = room_result.joined_count