`className` prop is not applied on `<Link />` component when generated with server-side rendering

Version

3.0.5

Steps to reproduce

1. Use server-side rendering with renderToString, RouterContext and match
2. Provide a className prop to <Link />

Expected Behavior

I expect to see the class attribute have the value of the className prop on the generated anchor tag.

Actual Behavior

The class attribute is missing on the generated anchor tag. Other className props are correctly applied on non-react-router components.

The match function:

/**
 * Use react-router's `match` to handle mapping inbound requests to the right prerendered component path
 * @see {@link https://github.com/ReactTraining/react-router/blob/master/docs/guides/ServerRendering.md}
 */
function ssr (req, res) {
  match({ routes, location: req.url }, (error, redirectLocation, renderProps) => {
    if (error) {
      return res.status(500).send(error.message)
    }

    if (redirectLocation) {
      return res.redirect(302, redirectLocation.pathname + redirectLocation.search)
    }

    let content
    if (renderProps) {
      // You can also check renderProps.components or renderProps.routes for
      // your "not found" component or route respectively, and send a 404 as
      // below, if you're using a catch-all route.
      content = renderToString(<RouterContext {...renderProps} />)
    } else {
      content = 'Not found'
      res.status(404)
    }

    return res.send(createPage(content))
  })
}

The <Link /> component with className prop:

<Link className='some-value' to={`/path/to/somewhere`}>Test</Link>

The output of this component:

<a href='/path/to/somewhere'>Test</a>

[timdorr]

This definitely works (I’ve done it in production a number of times). Something outside of the library or with your configuration is likely wrong, which falls into the category of a usage question.

[timdorr]

Here’s proof: https://codesandbox.io/s/20v898125p