code: public static Money zero(CurrencyUnit currency) {
          MoneyUtils.checkNotNull(currency, "Currency must not be null");
          BigDecimal bd = BigDecimal.valueOf(0, currency.getDecimalPlaces());
          return new Money(BigMoney.of(currency, bd));
      }
docs: Obtains an instance of {@code Money} representing zero.
  <p>
  For example, {@code zero(USD)} creates the instance {@code USD 0.00}.
  
  @param currency  the currency, not null
  @return the instance representing zero, never null