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**
expect(clientField === field).toBe(true);
          
          expect(clientField[valueKey]).toBe(changedValue);
        };
        it('should not blow away user-entered text on successful reconnect to an uncontrolled input', () =>
          testUserInteractionBeforeClientRender(
            <input defaultValue="Hello" />,
          ));
        it('should not blow away user-entered text on successful reconnect to a controlled input', async () => {
          let changeCount = 0;
          await testUserInteractionBeforeClientRender(
            <ControlledInput onChange={() => changeCount++} />,
          );
          
          
          
          expect(changeCount).toBe(0);
        });
        it('should not blow away user-entered text on successful reconnect to an uncontrolled checkbox', () =>
          testUserInteractionBeforeClientRender(
            <input type="checkbox" defaultChecked={true} />,
            true,
            false,
            'checked',
          ));
        it('should not blow away user-entered text on successful reconnect to a controlled checkbox', async () => {
          let changeCount = 0;
          await testUserInteractionBeforeClientRender(
            <ControlledCheckbox onChange={() => changeCount++} />,
            true,