1 files changed, 1 insertions, 1 deletions
diff --git a/synapse/storage/devices.py b/synapse/storage/devices.py
index 7b4213f20b..2db3ef4004 100644
--- a/synapse/storage/devices.py
+++ b/synapse/storage/devices.py
@@ -933,7 +933,7 @@ class DeviceStore(DeviceWorkerStore, BackgroundUpdateStore):
                     "ts": now,
                     "opentracing_context": json.dumps(context)
                     if whitelisted_homeserver(destination)
-                    else None,
+                    else "{}",
                 }
                 for destination in hosts
                 for device_id in device_ids