array_merge() : Fatal error when trying to create a custom group

[bastienho]

With PHP8+, when trying to create a custom group, I get this :

PHP Fatal error: Uncaught TypeError: array_merge(): Argument 1 must be of type array, null given in uk.co.compucorp.civicase/CRM/Civicase/Hook/BuildForm/AddStyleFieldToCaseCustomGroups.php:37

Stack trace:

1. /uk.co.compucorp.civicase/CRM/Civicase/Hook/BuildForm/AddStyleFieldToCaseCustomGroups.php(37): array_merge()
2. /uk.co.compucorp.civicase/civicase.php(236): CRM_Civicase_Hook_BuildForm_AddStyleFieldToCaseCustomGroups->run()
3. civicrm/civicrm/CRM/Utils/Hook.php(276): civicase_civicrm_buildForm()
4. civicrm/civicrm/CRM/Utils/Hook/WordPress.php(136): CRM_Utils_Hook->runHooks()
5. civicrm/civicrm/Civi/Core/CiviEventDispatcher.php(314): CRM_Utils_Hook_WordPress->invokeViaUF()
6. civicrm/civicrm/vendor/symfony/event-dispatcher/EventDispatcher.php(251): Civi\Core\CiviEventDispatcher::delegateToUF()
7. civicrm/civicrm/vendor/symfony/event-dispatcher/EventDispatcher.php(73): Symfony\Component\EventDispatcher\EventDispatcher->callListeners()
8. civicrm/civicrm/Civi/Core/CiviEventDispatcher.php(263): Symfony\Component\EventDispatcher\EventDispatcher->dispatch()
9. civicrm/civicrm/CRM/Utils/Hook.php(168): Civi\Core\CiviEventDispatcher->dispatch()
10. civicrm/civicrm/CRM/Utils/Hook.php(495): CRM_Utils_Hook->invoke()
11. civicrm/civicrm/CRM/Core/Form.php(744): CRM_Utils_Hook::buildForm()
12. civicrm/civicrm/CRM/Core/QuickForm/Action/Display.php(76): CRM_Core_Form->buildForm()
13. civicrm/civicrm/packages/HTML/QuickForm/Controller.php(203): CRM_Core_QuickForm_Action_Display->perform()
14. civicrm/civicrm/packages/HTML/QuickForm/Page.php(103): HTML_QuickForm_Controller->handle()
15. civicrm/civicrm/CRM/Core/Controller.php(355): HTML_QuickForm_Page->handle()
16. civicrm/civicrm/CRM/Utils/Wrapper.php(98): CRM_Core_Controller->run()
17. civicrm/civicrm/CRM/Core/Invoke.php(295): CRM_Utils_Wrapper->run()
18. civicrm/civicrm/CRM/Core/Invoke.php(69): CRM_Core_Invoke::runItem()
19. civicrm/civicrm/CRM/Core/Invoke.php(36): CRM_Core_Invoke::_invoke()
20. civicrm/civicrm.php(1199): CRM_Core_Invoke::invoke()