Custom property mapping sync error but still works

[CL107]

I have a custom property mapping for active directory used to map the UPN to the username. I also use a regex match to remove the domain on the end. This works and the users sync correctly, however the sync throws an error anyway:

Traceback (most recent call last): File "/authentik/sources/ldap/tasks.py", line 127, in ldap_sync count = sync_inst.sync(page) ^^^^^^^^^^^^^^^^^^^^ File "/authentik/sources/ldap/sync/groups.py", line 95, in sync raise StopSync(exc, None, exc.mapping) from exc authentik.lib.sync.outgoing.exceptions.StopSync: (PropertyMappingExpressionException(), None, <LDAPSourcePropertyMapping: AD UPN -> Username>)

This is my property mapping:

return {
    "username": regex_replace(ldap.get("userPrincipalName"), '@.*', ''),
}