Issue demo

Based on the ssr-caching demo. Adding a getServerSideProps hook to a page causes renderToHTML to send the response immediately and return null.

• Run npm run dev to start the server.
• Navigate to http://localhost:3000/
• See in the console that the rendered data is null, the headers were sent, and a finish event handler on the req is triggered even though we commented out the lines that send the response.

From packages/next/next-server/server/text-server.ts renderToHTMLWithComponents()

if (html && isServerProps) {
  sendPayload(res, html, 'html', {
    private: isPreviewMode,
    stateful: true, // GSSP request
  })
  return null
}