Jtl\Connector\Core\Http\JsonResponse::prepareAndSend() must be an instance of Jtl\Connector\Core\Rpc\ResponsePacket, null given, code example

Example: Jtl\Connector\Core\Http\JsonResponse::prepareAndSend() must be an instance of Jtl\Connector\Core\Rpc\ResponsePacket, null given,

// src/Controller/Product.php
namespace Acme\Connector\AcmeShop\Controller;

use Jtl\Connector\Core\Controller;
use Jtl\Connector\Core\Model\AbstractDataModel;

class Product implements PushInterface
{
    public function push(AbstractDataModel $model) : AbstractDataModel;
    {
        return $model;
    }
}