code: public static CurrencyUnit ofNumericCode(int numericCurrencyCode) {
          CurrencyUnit currency = currenciesByNumericCode.get(numericCurrencyCode);
          if (currency == null) {
              throw new IllegalCurrencyException("Unknown currency '" + numericCurrencyCode + '\'');
          }
          return currency;
      }
docs: Obtains an instance of {@code CurrencyUnit} for the specified ISO-4217 numeric currency code.
  <p>
  The numeric code is an alternative to the three letter code.
  
  @param numericCurrencyCode  the numeric currency code, not null
  @return the singleton instance, never null
  @throws IllegalCurrencyException if the currency is unknown