/**
  * Get url to access Next page of find
  * 
  * @return string or null
  */
 static function url_forward()
 {
     if (!empty(self::$url_forward)) {
         return self::$url_forward;
     }
     $next = self::page() + 1;
     if ($next > self::total_pages()) {
         return null;
     }
     $query = Request::query_get('page', $next);
     $url = explode('?', Url::$current);
     return self::$url_forward = $url[0] . '?' . $query;
 }