Problem is solved. I implemented the missing "?" to the code.

I wouldn't consider the issue resolved, since it's not acceptable for each user to have to modify the source code on their own.

The workaround you've applied doesn't solve the underlying problem, because if nothing is done, you'll be back in the same situation with the next update.

I've already described the problem here: https://www.joomshaper.com/forum/question/45852