Answer by Federico klez Culloca for How to handle "java.lang.IllegalArgumentException: rawPassword cannot be null"

Because it's throwing that exception before even reaching the point where it would throw a ConstraintViolationException.

Here

user.setPasword(bCryptPasswordEncoder.encode(userModel.getPasword()));

It's bCryptPasswordEncoder.encode(userModel.getPasword()) that is throwing the IllegalArgumentException, because it doesn't expect a null argument.