安装时joomla NULL响应

Question

<?php
/**
 * @package     Joomla.Installation
 * @subpackage  Controller
 *
 * @copyright   Copyright (C) 2005 - 2013 Open Source Matters, Inc. All rights reserved.
 * @license     GNU General Public License version 2 or later; see LICENSE.txt
 */

defined('_JEXEC') or die;

/**
 * Controller class to initialise the database for the Joomla Installer.
 *
 * @package     Joomla.Installation
 * @subpackage  Controller
 * @since       3.1
 */
class InstallationControllerInstallDatabase extends JControllerBase
{
    /**
     * Execute the controller.
     *
     * @return  void
     *
     * @since   3.1
     */
    public function execute()
    {
        // Get the application
        /* @var InstallationApplicationWeb $app */
        $app = $this->getApplication();

        // Check for request forgeries.
        JSession::checkToken() or $app->sendJsonResponse(new Exception(JText::_('JINVALID_TOKEN'), 403));

        // Get the setup model.
        $model = new InstallationModelSetup;

        // Get the options from the session
        $options = $model->getOptions();

        // Get the database model.
        $db = new InstallationModelDatabase;

        // Attempt to create the database tables.
        $return = $db->createTables($options);

        $r = new stdClass;
        $r->view = 'install';

        // Check if the database was initialised
        if (!$return)
        {
            $r->view = 'database';
        }

        $app->sendJsonResponse($r);
    }
}

这是执行的方法，响应是NULL，在JS端，脚本试图获取此对象的token属性NULL，我不知道为什么它来自NULL任何想法？

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