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**
});
  describe('dynamic injection', () => {
    beforeEach(() => {
      
      
      
      
      
      onAfterResetModules = () => {
        const DOMProperty = require('DOMProperty');
        DOMProperty.injection.injectDOMPropertyConfig({
          isCustomAttribute: function(name) {
            return name.indexOf('foo-') === 0;
          },
          Properties: {foobar: null},
        });
      };
      resetModules();
    });
    afterEach(() => {
      onAfterResetModules = null;
    });
    itRenders('injected attributes', async render => {
      const e = await render(<div foobar="simple" foo-xyz="simple" />, 0);
      expect(e.getAttribute('foobar')).toBe('simple');
      expect(e.getAttribute('foo-xyz')).toBe('simple');
    });
  });
});