BrowserOnly causes React error

[ianschmitz]

🐛 Bug Report

The BrowserOnly component returns undefined instead of null, which causes React to throw an error during a production build:

Error: Minified React error #152; visit https://reactjs.org/docs/error-decoder.html?invariant=152&args[]=BrowserOnly for the full message or use the non-minified dev environment for full errors and additional helpful warnings.Error: Minified React error #152; visit https://reactjs.org/docs/error-decoder.html?invariant=152&args[]=BrowserOnly for the full message or use the non-minified dev environment for full errors and additional helpful warnings.

This was changed in #2976.

Have you read the Contributing Guidelines on issues?

Yes

To Reproduce

Use BrowserOnly as suggested:

<BrowserOnly>{() => <Foo {...props} />}</BrowserOnly>

and run a production build of docusaurus.

Your Environment

• Docusaurus version used: 2.0.0-alpha.59
• Environment name and version (e.g. Chrome 78.0.3904.108, Node.js 10.17.0): Node 12.18.0
• Operating system and version (desktop or mobile): macOS 10.15.6

[slorber]

Thanks, totally agree: #3149