private Map<String, Quantity> loadStock() {
        if(stock == null) {
            stock = Maps.newConcurrentMap();
            declare(stock, "Coffee", 10);
            declare(stock, "Chocolate", 10);
            declare(stock, "OrangeJuice", 10);
            declare(stock, "Tea", 10);
            declare(stock, "TomatoPotage", 10);
        }
        return stock;
    }