Wordpress Multi - site Header & Footer Integration with vBulletin 5.0.x

[npadbidri]

Wordpress Multi - site Header & Footer Integration :

Hello,
I'm trying to integrate vBulletin 5.0.x with Wordpress.
Specifically, I'm trying to add the WordPress header and footer to show in vBulletin using Wordpress's functions get_header() and get_footer() that come from the file wp-blog-header.php in the WordPress installation folder. But my Wordpress site is a multi - site and I need header and footer of a particular website.

I have tried Wordpress header & footer integration with vBulletin 5.0.x for single website and It works fine.
I refer this post : Wordpress Header & Footer Integation for Wordpress header & footer integration with vBulletin 5.0.x for single website.

While intergration of Wordpress multi - site header & footer with vBulletin 5.0.x, I got following error :

Fatal error: Call to undefined method stdClass::escape() in \wp-content\sunrise.php.

################################################## ##
PHP code : (written into packages/extension/api/options.php)

PHP Code:

<?php

class wpHeaderFooter_Api_Options extends vB_Api_Extensions
{
    public $product = 'wpheaderfooter';
    public $version = '1.0.0';
    public $developer = 'me';
    public $title = 'WordPress Integration Extension';
    public $minver = '5.0.4';
    public $maxver = '5.1.3';
    public $infourl = '';
    public $checkurl = '';
    public $AutoInstall = 1;
    public $extensionOrder = 10;
    
    public function wpHeader(){
       define('ROOT_DIR',str_replace('\\\\', '/', realpath(dirname(__FILE__))).'/'); #Get real path for root dir ---linux and windows
        require_once(ROOT_DIR.'../testsite/wp-blog-header.php'); // get WordPress  
        get_header();        
    }
    
    public function wpFooter(){
        define('ROOT_DIR',str_replace('\\\\', '/', realpath(dirname(__FILE__))).'/'); #Get real path for root dir ---linux and windows
        require_once(ROOT_DIR.'../testsite/wp-blog-header.php'); // get WordPress  
        get_footer();
    }
}

So any help would be greatly appreciated.
Thanks!!!