/**
  * @param int $user_id
  * @return null|void
  */
 public function checkExternalUser($user_id = 0)
 {
     /**
      * @var $ilUser ilObjUser
      */
     global $ilUser;
     if (!(isset($user_id) && $user_id > 0)) {
         $user_id = $ilUser->getId();
     }
     //check if there is a xavc-login already saved in ilias-db
     $this->pluginObj->includeClass('class.ilXAVCMembers.php');
     $tmp_xavc_login = ilXAVCMembers::_lookupXAVCLogin($user_id);
     if (!$tmp_xavc_login) {
         $this->pluginObj->includeClass('class.ilAdobeConnectUserUtil.php');
         $xavc_login = ilAdobeConnectUserUtil::generateXavcLoginName($user_id);
         $externalLogin = ilXAVCMembers::addXAVCUser($user_id, $xavc_login);
     } else {
         // get saved login-data
         $externalLogin = $tmp_xavc_login;
     }
     return $externalLogin;
 }