Calling `ReactDOMServer.renderToStaticMarkup(elementWithPortal);` gets stuck in a loop while trying to do a static render.

Current behavior:
The behavior can be seen here: https://codepen.io/anon/pen/BmqWOM  by un-commenting line 58 (warning: this will make your tab freeze)

Expected behavior:
It should return with results or throw some kind of error if the input is not valid

render() {
          return null;
        }
      }
      var response = ReactDOMServer.renderToString(<NullComponent />);
      expect(response).toBe('');
    });
    
    it('should render composite components', () => {
      class Parent extends React.Component {
        render() {
          return (
            <div>
              <Child name="child" />
            </div>
          );
        }
      }
      class Child extends React.Component {