Don't include blank opentracing stuff in device list updates

Signed-off-by: Aaron Raimist <[email protected]>

Author: aaronraimist

synapse/storage/databases/main/devices.py

@@ -326,9 +326,11 @@ async def _get_device_update_edus_by_remote(
                     "device_id": device_id,
                     "prev_id": [prev_id] if prev_id else [],
                     "stream_id": stream_id,
-                    "org.matrix.opentracing_context": opentracing_context,
                 }
 
+                if opentracing_context != "{}":
+                    result["org.matrix.opentracing_context"] = opentracing_context
+
                 prev_id = stream_id
 
                 if device is not None: