lib/Model/OrderItem.php
public function setQuantity($quantity)
    {

        if (!is_null($quantity) && ($quantity <= 0)) {
            throw new \InvalidArgumentException('invalid value for $quantity when calling OrderItem., must be bigger than 0.');
        }

        $this->container['quantity'] = $quantity;

        return $this;
    }
public function setQuantity($quantity)
    {

        if (!is_null($quantity) && ($quantity <= 0)) {
            throw new \InvalidArgumentException('invalid value for $quantity when calling OrderItem., must be bigger than 0.');
        }

        $this->container['quantity'] = $quantity;

        return $this;
    }
Sets quantity
@param float $quantity
@return $this