public function decrementQuantityAt($cartItemIndex, $quantity = 1)
    {
        $this->existenceCheckFor($cartItemIndex);

        if ($this->items[$cartItemIndex]->quantity <= $quantity) {
            return $this->removeAt($cartItemIndex);
        }

        $this->items[$cartItemIndex]->quantity -= $quantity;

        $this->cartDriver->setCartItemQuantity(
            $this->items[$cartItemIndex]->id,
            $this->items[$cartItemIndex]->quantity
        );

        return $this->cartUpdates();
    }