docs: public static CurrencyUnit ofCountry(String countryCode) {
          MoneyUtils.checkNotNull(countryCode, "Country code must not be null");
          CurrencyUnit currency = currenciesByCountry.get(countryCode);
          if (currency == null) {
              throw new IllegalCurrencyException("No currency found for country '" + countryCode + '\'');
          }
          return currency;
      }