Registration not possible

-- HikaShop version -- : 4.2.1
-- Joomla version -- : 3.9.9
-- PHP version -- : 7.2.21
-- Browser(s) name and version -- : Chrome
-- Error-message(debug-mod must be tuned on) -- : 0 Call to a member function get() on null

User is not able to register. I am not sure it is Hikashop related, but i do not see someone reported problems about this in Joomla itself.

Another customer reported the same error message when accessing his cart. I could not reproduce that error.

I have included prints of both situations

Thank you Nicolas , it did at least for the reproducible problem