[5.2.3] Attempt to read property "parent" on array

[Quy]

Possibly from https://github.com/joomla/joomla-cms/pull/40665

@BrainforgeUK

Steps to reproduce the issue

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

[alikon]

please test #42237