Bean Validation 1.1 spec says:
While not mandatory, it is considered a good practice to split the core constraint validation from the not null constraint validation (for example, an @Email constraint will return true on a null object, i.e. will not take care of the @NotNull validation).

I suggest to change bean-validation-custom-constrain QS to be consistent with this recommendation:

1. AddressValidator should return true on null
2. @NotNull should be added to values where @Address must not be null