code: def validate_item_cmd(description, price, quantity, reference=None):
      
      return ValidateItemCmd(description=description, price=price, quantity=quantity, reference=reference)
docs: Create a commando to save items from the order.
      A list of items or commands must be created to save a order
      @param description: Item's description
      @param price: Item's price
      @param quantity: Item's quantity
      @param reference: a product reference for the item. Must be a Node
      @return: A Command that validate and save a item