On build 20220315:

Attempt to import an activity from one course to another.

Traceback:

[30-Mar-2022 11:02:58 Pacific/Auckland] Default exception handler: Exception - array_values(): Argument #1 ($array) must be of type array, null given Debug:
Error code: generalexceptionmessage

• line 687 of /availability/classes/tree.php: TypeError thrown
• line 687 of /availability/classes/tree.php: call to array_values()
• line 323 of /availability/classes/info.php: call to core_availability\tree->update_after_restore()
• line 926 of /backup/moodle2/restore_stepslib.php: call to core_availability\info->update_after_restore()
• line 34 of /backup/util/plan/restore_execution_step.class.php: call to restore_update_availability->define_execution()
• line 181 of /backup/util/plan/base_task.class.php: call to restore_execution_step->execute()
• line 191 of /backup/util/plan/base_plan.class.php: call to base_task->execute()
• line 168 of /backup/util/plan/restore_plan.class.php: call to base_plan->execute()
• line 394 of /backup/controller/restore_controller.class.php: call to restore_plan->execute()
• line 193 of /backup/import.php: call to restore_controller->execute_plan()

It seems this must be a bug rather than "just" duff data, as core_availability\info->update_after_restore() has just created a new tree, which uses decode_availability, which is supposed to either discard invalid data or throw an exception.

Attempting to replicate the problem on a dev instance, backing up and then restoring the course did complete successfully. Restoring the same backup onto the original prod instance did not succeed.