Steps to reproduce the issue

1- have a scheduled task
2- Set the task notifications to on and choose usergroup Super Users (default)
3- Make sure "receive system emails" is on for all users in Super Users group
4- Trigger the task

Expected result

All users in Super Users group should receive the task notification

Actual result

No user in Super Users group receives any notification.
Cron logs returns error:

In TaskNotification.php line 284:
                                                                               
  Joomla\Plugin\System\TaskNotification\Extension\TaskNotification::sendMail(  
  ): Argument #4 ($groups) must be of type array, null given, called in /srv/  
  myjoomla/plugins/system/tasknotification/src/Extension/TaskNotification.p  
  hp on line 200

System information (as much as possible)

dbserver: mysql
dbversion: 10.11.11-MariaDB-0+deb12u1
dbcollation: utf8mb4_roman_ci
dbconnectioncollation: utf8mb4_general_ci
dbconnencryptsupported: false
phpversion: 8.2.28
server: Apache
sapi_name: fpm-fcgi
version: Joomla! 5.3.0 Stable [ Timu ] 15-April-2025 16:00 GMT
compatpluginenabled: true
compatpluginparameters:

Additional comments

Maybe related to #44604 ?