Next.js: Error: Cannot read property '__html' of undefined when defining a custom Document with getInitialProps

[markbrocato]

Bug report

Describe the bug

If you defined a pages/_document.js with getInitialProps, and return styles, you get this error when loading the app with ?amp=1 in the URL:

Error: Cannot read property '__html' of undefined when defining a custom Document.getInitialProps

To Reproduce

Use the _document.js from Material UI's example here: https://github.com/mui-org/material-ui/blob/master/examples/nextjs/pages/_document.js

The error goes away if you comment out:

    styles: [
      <React.Fragment key="styles">
        {initialProps.styles}
        {sheets.getStyleElement()}
      </React.Fragment>,
    ],

Expected behavior

An AMP response should be rendered without error.

Screenshots

System information

• OS: macOS
• Browser: chrome
• Version of Next.js: 9.1.1

[Janpot]

related:
https://github.com/zeit/next.js/issues/9041
https://github.com/zeit/next.js/issues/7856

[timneutkens]

Going to close this issue as it hasn't had activity for a few months. I believe the issue has been fixed by Olivier 👍