app.render returns undefined in SSR cache example

[prasanna1211]

Bug report

Describe the bug

In the SSR cache example, exactly in this line the data seems to be undefined when debugging. Because of this the SSR response couldn't be cached.

const ssrCache = cacheableResponse({
  ttl: 1000 * 60 * 60, // 1hour
  get: async ({ req, res }) => {

   // --> The value of data is always null
    const data = await app.render(req, res, req.path, {
      ...req.query,
      ...req.params,
    })

    // Add here custom logic for when you do not want to cache the page, for
    // example when the page returns a 404 status code:
    if (res.statusCode === 404) {
      res.end(data)
      return
    }

    return { data }
  },
  send: ({ data, res }) => res.send(data),
})

The value of data should actually be the response HTML that gets cached.

To Reproduce

1. curl https://codeload.github.com/vercel/next.js/tar.gz/canary | tar -xz --strip=2 next.js-canary/examples/ssr-caching
2. cd ssr-caching
3. npm install and npm run dev

Expected behavior

The value of data should actually be the response HTML that gets cached in the next step.

Screenshots

System information

• OS: Mac OS
• Browser: Chrome
• Version of Next.js: 9.5.2
• Version of Node.js: 12.16.3

Additional context

An unhandledPromiseRejection error is thrown due to the data being undefined.

[SiZapPaaiGwat]

Yeah, got the same problem.The example does not work.

[leerob]

#18786

[balazsorban44]

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