    public function gc($maxlifetime)
    {
        $this->getCollection()->remove(array(
            $this->options['expiry_field'] => array('$lt' => new \MongoDate()),
        ));

        return true;
    }
The software constructs all or part of an SQL command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended SQL command when it is sent to a downstream component.