CartThrob checkout error - Call to undefined method stdClass::set()

The CartThrob Support team managed to solve this problem I’ve been having. When attempting to process new orders, I was getting the following error, when running CT 6.0.2

Call to undefined method stdClass::set()
cartthrob_entries_model.php:407

It turns out this was happening only when placing orders as a logged-out user.

As I had no value entered in CT Settings for the “Logged Out Member ID (leave blank to default to oldest superadmin)” it was tripping over, and not falling-back to use the described “oldest superadmin” ID. This was working in the CT5 version of my site, but this bug is now being fixed in CT6.

By simply manually adding a Member ID in that Setting, everything now works fine.