autocde2.0/app/Services/Notification/ActionBrowser/TaskNotification.php

<?php

namespace App\Services\Notification\ActionBrowser;

use App\Services\Notification\Abstracts\ActionBrowserNotificationAbstract;

class TaskNotification extends ActionBrowserNotificationAbstract
{
    protected function userIDs(): array
    {
        $assignArray=isset($this->object->assign)?$this->object->assign:[];
        $mailtoArray=isset($this->object->mailto)?$this->object->mailto:[];
        return (!empty($assignArray) || !empty($mailtoArray)) ? array_unique(array_merge($assignArray, $mailtoArray)) : [];
    }
}