code: def add_register_user(
          self, username, first_name, last_name, email, password="", hashed_password=""
      ):
          
          register_user = self.registeruser_model()
          register_user.username = username
          register_user.email = email
          register_user.first_name = first_name
          register_user.last_name = last_name
          if hashed_password:
              register_user.password = hashed_password
          else:
              register_user.password = generate_password_hash(password)
          register_user.registration_hash = str(uuid.uuid1())
          try:
              self.get_session.add(register_user)
              self.get_session.commit()
              return register_user
          except Exception as e:
              log.error(c.LOGMSG_ERR_SEC_ADD_REGISTER_USER.format(str(e)))
              self.appbuilder.get_session.rollback()
              return None
docs: Add a registration request for the user.
  
              :rtype : RegisterUser