Allow to set null currency for product discount

Author: yushkevich

NetLicensingClient/src/main/java/com/labs64/netlicensing/schema/converter/ItemToProductConverter.java

@@ -49,7 +49,9 @@ public Product convert(final Item source) throws ConversionException {
                 final ProductDiscountImpl productDiscount = new ProductDiscountImpl();
                 final Money price = convertPrice(list.getProperty(), Constants.Product.Discount.TOTAL_PRICE);
                 productDiscount.setTotalPrice(price.getAmount());
-                productDiscount.setCurrency(price.getCurrencyCode());
+                if (price.getCurrencyCode() != null) {
+                    productDiscount.setCurrency(price.getCurrencyCode());
+                }
                 if (SchemaFunction.propertyByName(list.getProperty(), Constants.Product.Discount.AMOUNT_FIX).getValue() != null) {
                     final Money amountFix = convertPrice(list.getProperty(), Constants.Product.Discount.AMOUNT_FIX);
                     productDiscount.setAmountFix(amountFix.getAmount());