React 16 alpha allows returning array in render function but server renderer expects children to always be react elements

```
TypeError: Cannot read property 'toLowerCase' of undefined
    at ReactDOMServerRenderer.renderDOM
```

source
```javascript
function renderDOM(element, context) {
    var tag = element.type.toLowerCase(); // element is array
```

Fiddle: https://jsfiddle.net/84v837e9/160/

**react@16.0.0-alpha.13**
getTitle = () => {
        return this.props.title;
      };
      render() {
        return this.props.getContent();
      }
    }
    var mounted = false;
    class Component extends React.Component {
      getInner = () => {
        
        
        return <div className="inner" ref={c => (this.innerRef = c)} />;
      };
      render() {
        return (
          <Wrapper
            title="wrapper"
            ref={c => (this.wrapperRef = c)}
            getContent={this.getInner}
          />
        );
      }
      componentDidMount() {