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.
tagVerbatim: string,
  tagLowercase: string,
  props: Object,
  namespace: string,
  makeStaticMarkup: boolean,
  isRootElement: boolean,
): string {
  let ret = '<' + tagVerbatim;
  for (const propKey in props) {
    if (!props.hasOwnProperty(propKey)) {
      continue;
    }
    let propValue = props[propKey];
    if (propValue == null) {
      continue;
    }
    if (propKey === STYLE) {
      propValue = createMarkupForStyles(propValue);
    }
    let markup = null;
    if (isCustomComponent(tagLowercase, props)) {
      if (!RESERVED_PROPS.hasOwnProperty(propKey)) {
        markup = createMarkupForCustomAttribute(propKey, propValue);