public function merge(RouterInterface $source = null)
    {
        if (null == $source) {
            return [
                $this->routes,
                $this->defaultParams,
            ];
        }
        list($routes, $params) = $source->merge();

        $this->routes        = array_merge($this->routes, $routes);
        $this->defaultParams = array_merge($this->defaultParams, $params);
    }