code: private BigMoney checkCurrencyEqual(BigMoneyProvider moneyProvider) {
          BigMoney money = of(moneyProvider);
          if (isSameCurrency(money) == false) {
              throw new CurrencyMismatchException(getCurrencyUnit(), money.getCurrencyUnit());
          }
          return money;
      }
docs: Validates that the currency of this money and the specified money match.
  
  @param moneyProvider  the money to check, not null
  @throws CurrencyMismatchException if the currencies differ