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.
render() {
            return [null, [<Y key="1" />], false];
          }
        }
        function Y() {
          return [<Z key="1" />, ['c']];
        }
        function Z() {
          return null;
        }
        const e = await render(
          <div>
            {[['a'], 'b']}
            <div>
              <X key="1" />
              d
            </div>
            e
          </div>,
        );
        if (
          render === serverRender ||
          render === clientRenderOnServerString ||
          render === streamRender