I'm not sure if I understood that.
Do you expect to be able to set a backing bean property value to null directly from a JSF form? How yo you expect the user to enter a null into a web page? Beyond that, web pages are text, so a null can never appear on a web page because null is a binary object.
When a user leaves a field blank on a web page, what is posted to the backing bean is an empty
string (""), not a null.
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.