def find_item(item)
      return nil if cart_items.blank?

      item = prepare_for_cart_item(item)
      result = cart_items.detect do |ci|
        ci.type == item.type && ci.unit == item.unit
      end
      return result.nil? ? false : result
    end
def find_item(item)
      return nil if cart_items.blank?

      item = prepare_for_cart_item(item)
      result = cart_items.detect do |ci|
        ci.type == item.type && ci.unit == item.unit
      end
      return result.nil? ? false : result
    end
searches cart_items by a given Hash or MongoidCart::ActsAsProduct instance