Customized error in REST – response entity’s body is null even though error was thrown

I have the following REST endpoint:

Customized error in REST – response entity’s body is null even though error was thrown

I have the following REST endpoint:

Why is saveUserWithExceptionHandling() method working when trying to create User but it doesnt when trying to edit

When creating Error Handlers I have come accross this situation, when editing or creating an user I have to make sure that CPF and EMAIL are unique, so I created this method