Observed this on react@16.0.0-beta.5

```js
import React from 'react';
import { renderToString } from 'react-dom/server';

const B = () => 'b';

console.log(renderToString(<div>{'a'}<B />{'c'}</div>));
```

This renders as `<div data-reactroot="">a<!-- -->bc</div>`. If you try to hydrate this you'll get the error: Text content did not match. Server: "bc" Client: "b".
var serialized = '';
  var delimiter = '';
  for (var styleName in styles) {
    if (!styles.hasOwnProperty(styleName)) {
      continue;
    }
    var isCustomProperty = styleName.indexOf('--') === 0;
    var styleValue = styles[styleName];
    if (__DEV__) {
      if (!isCustomProperty) {
        warnValidStyle(styleName, styleValue, component);
      }
    }
    if (styleValue != null) {
      serialized += delimiter + processStyleName(styleName) + ':';
      serialized += dangerousStyleValue(
        styleName,
        styleValue,
        isCustomProperty,
      );
      delimiter = ';';
    }
  }
  return serialized || null;
}
function warnNoop(