code: public Properties putProducts(Product... products) {
      if (isNullOrEmpty(products)) {
        throw new IllegalArgumentException("products cannot be null or empty.");
      }
      List<Product> productList = new ArrayList<>(products.length);
      Collections.addAll(productList, products);
      return putValue(PRODUCTS_KEY, Collections.unmodifiableList(productList));
    }
docs: Set the individual products for an order associated with an event.
  
  @see <a href="https://segment.com/docs/api/tracking/ecommerce/">Ecommerce API</a>