I'm struggling with an error which I can't understand, my site has a reserved area to which users should register, when they press on "register" the system gives "0 call to a member action get () null". If I login with a registered user (registered via backend) and try to open the profile page to edit its profile I get the same error. If I open the same page with my account (superuser) I don't get any problem.
It's been 7 days I'm looking on the internet to find a solution.
My joomla version is 3.9.1 + 7.1 php
Thank you in advance to those who will try to help me!