code: protected final void registerCountry(String countryCode, String currencyCode) {
          CurrencyUnit.registerCountry(countryCode, CurrencyUnit.of(currencyCode));
      }
docs: Registers a country allowing it to be used.
  <p>
  This method is called by {@link #registerCurrencies()} to perform the
  actual creation of a country.
  
  @param countryCode  the country code, not null
  @param currencyCode  the currency code, not null