docs: public BigMoney minus(BigDecimal amountToSubtract) {
          MoneyUtils.checkNotNull(amountToSubtract, "Amount must not be null");
          if (amountToSubtract.compareTo(BigDecimal.ZERO) == 0) {
              return this;
          }
          BigDecimal newAmount = amount.subtract(amountToSubtract);
          return BigMoney.of(currency, newAmount);
      }