public function setSessionCart(Cart $cart = null)
    {
        if (null === $cart || $cart->isNew()) {
            self::$transientCart = $cart;
            $this->remove("thelia.cart_id");
        } else {
            self::$transientCart = null;
            $this->set("thelia.cart_id", $cart->getId());
        }

        return $this;
    }