code: public static CurrencyFunction currency(Field field, @Nullable String currencyCode) {
  
  		Assert.notNull(field, "Field for currency function must not be 'null'.");
  
  		CurrencyFunction function = new CurrencyFunction(field);
  		if (StringUtils.hasText(currencyCode)) {
  			function.addArgument(currencyCode);
  		}
  		return function;
  	}
docs: Create new {@link CurrencyFunction} using ISO-4217 currencyCode representing
  {@code currency(fiel.getName(),currencyCode)}
  
  @param field
  @param currencyCode
  @return