Possibly from #40665

@BrainforgeUK

Steps to reproduce the issue

Enable Maximum Reporting.
Go to System > Administrator Template Styles.
Edit Atum - Default.
Click Save button.
See PHP error log.

Actual result

PHP Warning:  Attempt to read property "parent" on array in \administrator\components\com_templates\src\Model\StyleModel.php on line 399
PHP Warning:  Attempt to read property "parent" on array in \administrator\components\com_templates\src\Model\StyleModel.php on line 400
PHP Warning:  Attempt to read property "parent" on array in \administrator\components\com_templates\src\Model\StyleModel.php on line 400