Error in array_reverse: Argument 1 must be of type array, null given

[rajandangi]

Execute scheduled task: Cleanup contexts (core\task\context_cleanup_task)
... started 18:20:38. Current memory use 5.0 MB.
... used 28 dbqueries
... used 2.8978610038757 seconds
Scheduled task failed: Cleanup contexts (core\task\context_cleanup_task),array_reverse(): Argument #1 ($array) must be of type array, null given
Backtrace:
* line 376 of /grade/grading/form/rubric_ranges/lib.php: call to array_reverse()
* line 99 of /grade/grading/form/lib.php: call to gradingform_rubric_ranges_controller->load_definition()
* line 530 of /grade/grading/lib.php: call to gradingform_controller->__construct()
* line 613 of /grade/grading/lib.php: call to grading_manager->get_controller()
* line 5564 of /lib/accesslib.php: call to grading_manager::delete_all_for_context()
* line 5604 of /lib/accesslib.php: call to context->delete_content()
* line 6125 of /lib/accesslib.php: call to context->delete()
* line 47 of /lib/classes/task/context_cleanup_task.php: call to context_helper::cleanup_instances()
* line 309 of /lib/cronlib.php: call to core\task\context_cleanup_task->execute()
* line 120 of /lib/cronlib.php: call to cron_run_inner_scheduled_task()
* line 73 of /lib/cronlib.php: call to cron_run_scheduled_tasks()
* line 178 of /admin/cli/cron.php: call to cron_run()

Testing:

php admin/cli/scheduled_task.php --execute=core\\task\\context_cleanup_task