sources/ldap: prevent error when retrying old system task with no arguments

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

authentik/sources/ldap/tasks.py

@@ -1,4 +1,6 @@
 """LDAP Sync tasks"""
+from typing import Optional
+
 from django.utils.text import slugify
 from ldap3.core.exceptions import LDAPException
 from structlog.stdlib import get_logger
@@ -29,7 +31,8 @@ def ldap_sync_all():
 @CELERY_APP.task(
     bind=True, base=MonitoredTask, soft_time_limit=60 * 60 * 2, task_time_limit=60 * 60 * 2
 )
-def ldap_sync(self: MonitoredTask, source_pk: str, sync_class: str):
+# TODO: remove Optional[str] in 2021.10
+def ldap_sync(self: MonitoredTask, source_pk: str, sync_class: Optional[str] = None):
     """Synchronization of an LDAP Source"""
     self.result_timeout_hours = 2
     try:
@@ -38,6 +41,8 @@ def ldap_sync(self: MonitoredTask, source_pk: str, sync_class: str):
         # Because the source couldn't be found, we don't have a UID
         # to set the state with
         return
+    if not sync_class:
+        return
     sync = path_to_class(sync_class)
     self.set_uid(f"{slugify(source.name)}-{sync.__name__}")
     try: