code: private function __next(ServerRequestInterface $request, ResponseInterface $response, $next)
      {
          $this->__loadConfigFiles();
  
          return $next($request, $response);
      }
docs: Calls the next middleware.
  
  @param ServerRequestInterface $request  The request.
  @param ResponseInterface $response The response.
  @param callable $next The next middleware to call.
  
  @return \Psr\Http\Message\ResponseInterface A response.