This might be a reference to this one: https://github.com/facebook/react/issues/10212#issuecomment-346302374

The problem still exist.

So, trying to render with server side and got this error. I don't have this notation in my code but this might be a problem with dependencies.

```
TypeError: Cannot read property 'toLowerCase' of undefined
    at ReactDOMServerRenderer.renderDOM (/Users/lukasborawski/Dev/web-client/node_modules/react-dom/cjs/react-dom-server.node.development.js:2304:27)
...
```

```
"react": "^16.1.1",
"react-dom": "^16.2.0",
```

Thx for help.
let content = '';
  
  
  React.Children.forEach(children, function(child) {
    if (child == null) {
      return;
    }
    if (typeof child === 'string' || typeof child === 'number') {
      content += child;
    } else {
      if (__DEV__) {
        if (!didWarnInvalidOptionChildren) {
          didWarnInvalidOptionChildren = true;
          warning(
            false,
            'Only strings and numbers are supported as <option> children.',
          );
        }
      }
    }
  });
  return content;
}
function maskContext(type, context) {