diff --git a/SAS/TMSS/backend/src/tmss/tmssapp/subtasks.py b/SAS/TMSS/backend/src/tmss/tmssapp/subtasks.py
index ecfc1b6e0f3e367972a5ea604131f8bae7c2ad86..0bdfdf731b5dc9c5c23e93b549cf8f9787c087f7 100644
--- a/SAS/TMSS/backend/src/tmss/tmssapp/subtasks.py
+++ b/SAS/TMSS/backend/src/tmss/tmssapp/subtasks.py
@@ -1688,7 +1688,8 @@ def convert_task_station_groups_specification_to_station_list_without_used_and_o
 
     if remove_reserved_stations:
         # get overlapping reserved_stations
-        scheduler = subtask.task_blueprint.scheduling_unit_blueprint.scheduling_constraints_doc.get('scheduler', '')
+        sub = subtask.task_blueprint.scheduling_unit_blueprint
+        scheduler = sub.scheduling_constraints_doc.get('scheduler', '') if sub.scheduling_constraints_doc is not None else ''
         reserved_stations = set(get_reserved_stations_in_timewindow(lower_bound=subtask.scheduled_start_time,
                                                                     upper_bound=subtask.scheduled_stop_time,
                                                                     ignore_reservations_allowing_scheduling_for_project=subtask.project,