Example of a Header error, message: Uncaught TypeError: Cannot read property 'type' of null

index.js

import React from 'react';
import { Layout, Content, Navigation, Button, Header } from 'react-mdl';
import 'react-mdl/extra/material.js';
import 'react-mdl/extra/material.css';

React.render(
  <Layout fixedHeader>
  <Header transparent title="Demo">
    {false && <Button raised colored>LOG IN</Button>}
    <Navigation className="header-navigation">
      <div>REPORTS</div>
      <div>LOG OUT</div>
    </Navigation>
  </Header>
  <Content />
  </Layout>,
  document.body
);