Criteria criteria = session.createCriteria(User.class);
criteria.add(
        Restrictions.and(
        Restrictions.ilike("firstName", firstName),
        Restrictions.ilike("lastName", lastName)
        )
    );

def userList = userCriteria.list{
    and{
        if(firstName) {
            like('firstName',firstName)
        }
        if(lastName) {
            like('lastName',lastName)
        }
       }
}