title: How to extends material-ui component
body: <p>I want to exetend <strong>Tab</strong> component with <strong>es6 class</strong> like this:</p>
  
  <pre class="lang-js prettyprint-override"><code>import React from "react";
  
  import {Tab} from "material-ui";
  
  class MyTab extends Tab {
      constructor(props){
          super(props);
      }
  
      render(){
          return super.render();
      }
  
  }
  
  export default MyTab;
  </code></pre>
  
  <p>But i get an error:</p>
  
  <pre><code>Uncaught TypeError: Cannot read property 'muiTheme' of undefined
  </code></pre>
  
  <p>What am I doing wrong?</p>