docs: public BigMoney multiplyRetainScale(BigDecimal valueToMultiplyBy, RoundingMode roundingMode) {
          MoneyUtils.checkNotNull(valueToMultiplyBy, "Multiplier must not be null");
          MoneyUtils.checkNotNull(roundingMode, "RoundingMode must not be null");
          if (valueToMultiplyBy.compareTo(BigDecimal.ONE) == 0) {
              return this;
          }
          BigDecimal newAmount = amount.multiply(valueToMultiplyBy);
          newAmount = newAmount.setScale(getScale(), roundingMode);
          return BigMoney.of(currency, newAmount);
      }