title: Stateless function components cannot be given refs
body: <p>I try to access some refs in my component. But I have this error in the console.
  <code>withRouter.js:44 Warning: Stateless function components cannot be given refs (See ref "pseudo" in FormInputText created by RegisterForm). Attempts to access this ref will fail.</code></p>
  
  <p>Here is my component:</p>
  
  <pre><code>class RegisterForm extends React.Component {
  
    render() {
      return (
        &lt;form action=""&gt;
          &lt;FormInputText ref="pseudo"  type="text" defaultValue="pseudo"/&gt;
          &lt;input type="button" onClick={()=&gt;console.log(this.refs);} value="REGISTER"/&gt;
        &lt;/form&gt;
      );
    }
  }
  </code></pre>
  
  <p>Plus when I click on the button I got <code>Object {pseudo: null}</code>in the console. I would expect an object instead <code>null</code>.</p>
  
  <p>I am not sure to understand why this is not working. Note that my react tree uses <code>mobx-react</code>.</p>