NotifyUrl workaround

Paypal.php

<?php

$agreement = new HackAgreement();
// ...
$agreement->create($apiContext);

////////////

use PayPal\Api\Agreement;

class HackAgreement extends Agreement
{
    /**
     * Plan details for this agreement.
     *
     * @return \HackNamespace\HackPlan
     */
    public function getPlan()
    {
        return parent::getPlan();
    }
}

////////////

use PayPal\Api\Plan;

class HackPlan extends Plan
{
    /**
     * Specific preferences such as: set up fee, max fail attempts, autobill amount, and others that are configured for this billing plan.
     *
     * @return \HackNamespace\HackMerch
     */
    public function getMerchantPreferences()
    {
        return parent::getMerchantPreferences(); // TODO: Change the autogenerated stub
    }
}

////////////

use PayPal\Api\MerchantPreferences;

class HackMerch extends MerchantPreferences
{
    public function setNotifyUrl($notifyUrl)
    {
        if (!$notifyUrl) {
            return $this;
        }

        return parent::setNotifyUrl($notifyUrl);
    }
  
    public function setCancelUrl($notifyUrl)
    {
        if (!$notifyUrl) {
            return $this;
        }

        return parent::setCancelUrl($notifyUrl);
    }

    public function setReturnUrl($notifyUrl)
    {
        if (!$notifyUrl) {
            return $this;
        }

        return parent::setReturnUrl($notifyUrl);
    }
}