title: TypeError : React object is undefined on createElement
body: <p>I am new to <code>React</code> and <code>Material UI</code> and I am attempting to create an <code>AppBar</code> with <code>Tabs</code> as children. My current implementation looks like this:</p>
  
  <pre><code>import {React, PropTypes, Component} from 'react';
  import TodoTextInput from './TodoTextInput';
  import injectTapEventPlugin from 'react-tap-event-plugin';
  import baseTheme from 'material-ui/styles/baseThemes/lightBaseTheme'
  import getMuiTheme from 'material-ui/styles/getMuiTheme'
  import {Tabs, Tab} from 'material-ui/Tabs';
  import {AppBar} from 'material-ui/AppBar';
  
  const styles = {
    headline: {
      fontSize: 24,
      paddingTop: 16,
      marginBottom: 12,
      fontWeight: 400
    }
  };
  
  function handleActive(tab) {
    alert(`A tab with this route property ${tab.props['data-route']} was activated.`);
  }
  const defaultStyle = {
    marginLeft: 20
  };
  
  class Header extends Component {
    render() {
      return (
        &lt;header className="header"&gt;
        &lt;AppBar title="TEST" /&gt;
          &lt;Tabs&gt;
            &lt;Tab label="Tab 1" &gt;
              &lt;div&gt;
  
              &lt;/div&gt;
            &lt;/Tab&gt;
            &lt;Tab label="Tab 2" &gt;
              &lt;div&gt;
  
              &lt;/div&gt;
            &lt;/Tab&gt;
            &lt;Tab label="Tab 3" &gt;
              &lt;div&gt;
  
              &lt;/div&gt;
            &lt;/Tab&gt;
            &lt;Tab label="Tab 4" &gt;
              &lt;div&gt;
  
              &lt;/div&gt;
            &lt;/Tab&gt;
          &lt;/Tabs&gt;
          {children}
        &lt;/header&gt;
      );
    }
  }
  
  module.exports = Header;
  </code></pre>
  
  <p>I'm getting an error that states:</p>
  
  <pre><code>TypeError: undefined is not an object (evaluating '_react.React.createElement')
  </code></pre>
  
  <p>I am unsure on how to fix this problem. Please help!</p>