Undefined array key "list_type" – TYPO3 13 compatible branch

[seitenformate]

Create a new content element in backend e.g. type "menu_subpages" leads to following error

503 Oops, an error occurred! PHP Warning: Undefined array key "list_type" in /var/www/html/vendor/extcode/cart-events/Classes/Hooks/DatamapDataHandlerHook.php line 50

• TYPO3 13
• cart_event version: typo3-13-compatible
• composer; ddev/docker environment

Possible solution may be something like that:

...
$listType = $incomingFieldArray['list_type'] ?? null;
$pageDoktype = $page['doktype'] ?? 0;

if (!$this->isAllowedTargetPage($listType, $pageDoktype)) {
...