Draft: [FIX] Notice: Undefined index: cat_categories

here two possibilities are open to us. first the error comes from the fact that the categories can either not exist or be chosen, tiki will create the calendar. now to avoid this error we can either make the choice of categories mandatory which will probably disturb those who don't put any or just check if the category is chosen and send it null if not.

https://app.glitchtip.com/evoludata/issues/1780447?project=2583&query=is:unresolved&sort=-priority&cursor=cD01NTg5LjQ4NTU2NTM5Mzc1Nw%3D%3D and https://avan.tech/item68774-Fix-all-errors-in-logs-that-are-not-related-to-Cypht-Webmail-Smarty-icons-and-menus-was-Use-the-GlitchTip-error-reporting-as-a-perpetual-to-do-list-for-junior-developers