private function getShownExtension()
    {
        if($this->hasRequestParameter('shownExtension')){
            $shownExtension = $this->getRequestParameter('shownExtension');
            if(strlen(trim($shownExtension)) > 0){
                $extension = $this->getExtension($shownExtension);
                return $extension->getName();
            }
        }
        return null;
    }