public function listRefunds(Payplug\Payplug $payplug = null)
    {
        if (!array_key_exists('id', $this->getAttributes())) {
            throw new Payplug\Exception\InvalidPaymentException("This payment object has no id. You can't list refunds on it.");
        }

        return Refund::listRefunds($this->id, $payplug);
    }