Joomla Update 6.1

-- HikaShop version -- : 6.1.1
-- Joomla version -- : 6.1
-- PHP version -- : 8.4
-- Browser(s) name and version -- : Firefox
-- Error-message(debug-mod must be tuned on) -- : Error: 0 call to a member function gettype {} on null

Hi
I installed the Joomla 6.1 update.
Since then, emails have stopped sending. Instead, the error message “Error: 0 call to a member function gettype {} on null” appears.
Was kann ich tun?
Thanks for your help
langi