public void validateCity(String cityCode) {
        Optional<City> city = findCity(cityCode);
        if (city.isPresent()) {
            return;
        }
        setError(CITY_INVALID, cityCode);
    }

    public Optional<City> findCity(String cityCode) {
        City city = cityRepository.get(cityCode);
        return Optional.ofNullable(city);
    }