Signup goes to http500 error if no userlicense avaliable

if I try to sign up (public) to my server (PRO) and there are all userlicenses in use,
the browser edge displays a http500 error.

chrome:

Page unavailable
Sorry, but the requested page is unavailable due to a server hiccup.
Our engineers have been notified, so check back later.

I think a more handy way would be, setting the user to inactive and send an email to admin.