The first commit is a workaround.

Let the ticket open until CMS-9541 is fixed, and then revert it (and propose a migration script)

What is happening is that currently, Ametys cannot see the difference between an empty value for an optional parameter (not present in purpose) and the absence of the value because it is a 'new' parameter (user never had the opportunity to fill it). Thus, as the optional parameter defines a default value, when editing the service, the default value is automatically filled for those parameters which are empty whereas we do not want.