Fix: unexpected operation of document management (#10366)

### What problem does this PR solve?

 Unexpected operation of document management.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/db/services/user_service.py

@@ -315,4 +315,4 @@ class UserTenantService(CommonService):
             ).first()
             return user_tenant
         except peewee.DoesNotExist:
-            return None
+            return None