public function mk($key, $value, $ttl = 0)
    {
        $body = $request = $this->set(
            $key,
            $value,
            $ttl,
            array('prevExist' => 'false')
        );

        if (isset($body['errorCode'])) {
            throw new KeyExistsException($body['message'], $body['errorCode']);
        }

        return $body;
    }