code: protected function transform($middleware, $wrappable = true)
      {
          if (is_a($middleware, Application::MIDDLEWARE) === false) {
              $approach = (boolean) $this->approach($middleware);
  
              $response = $approach === self::SINGLE_PASS ? $this->response : null;
  
              $wrapper = new CallableMiddlewareWrapper($middleware, $response);
  
              $middleware = $wrappable === true ? $wrapper : $middleware;
          }
  
          return $middleware;
      }
docs: Transforms the specified middleware into a PSR-15 middleware.
  
  @param  \Interop\Http\ServerMiddleware\MiddlewareInterface|\Closure $middleware
  @param  boolean                                                     $wrappable
  @return \Interop\Http\ServerMiddleware\MiddlewareInterface