message: allow null as registration data
diff: @@ -27,7 +27,7 @@ router.post('/register', async (req, res, next) => {
  const schema = Joi.object().keys({
  username: Joi.string().required(),
  password: Joi.string().required(),
  - register_data: Joi.object(),
  + register_data: Joi.object().allow(null),
  });
  const { error, value } = schema.validate(req.body);
  