public function isValid($value)
    {
        if ($value == $this->allowName) {
            return true;
        }
        
        foreach ($this->getUser()->getGroups() as $group) {
            if ($group->getName() == $value) {
                $this->error(self::MSG_NOT_UNIQUE, $value);
                return false;
            }
        }
        return true;
    }