protected function _autoload($class)
    {
        $callback = $this->getDefaultAutoloader();
        try {
            if ($this->suppressNotFoundWarnings()) {
                @call_user_func($callback, $class);
            } else {
                call_user_func($callback, $class);
            }
            return $class;
        } catch (Zend_Exception $e) {
            return false;
        }
    }