@Override
 public void addUsers(User user) throws UserAlreadyExistsException, PasswordIsTooWeakException {
   try {
     hasUser(user.getUsername());
   } catch (UserUnknownException e) {
     super.addUsers(user);
     return;
   }
   throw new UserAlreadyExistsException(user.getUsername());
 }
 protected void remove() {
   getSlash();
   for (User user : super.getUsersSet()) {
     this.removeUsers(user.getUsername());
     user.remove();
   }
   deleteDomainObject();
 }
 public User getUserByUsername(String username) throws UserUnknownException {
   for (User user : super.getUsersSet()) {
     if (user.getUsername().equals(username)) return user;
   }
   throw new UserUnknownException(username);
 }