protected function addControlsToString($ldif)
    {
        foreach ($this->controls as $control) {
            $value = $control->getOid().' '.$control->getCriticality();
            if (!is_null($control->getValue())) {
                $value .= ' '.$control->getValue();
            }
            $ldif .= $this->getLdifLine(Ldif::DIRECTIVE_CONTROL, $value);
        }

        return $ldif;
    }