title: React Router v4 - Error: React.Children.only expected to receive a single React element child
body: <p>I'm using react router v4 in a very simple app. I've tried to follow the documentation but I have a weird error when my app try to launch.</p>
  
  <p>The error says: <code>error: React.Children.only expected to receive a single React element child</code></p>
  
  <p>The weird thing is that I have only one component in my ReactDOM.render function.</p>
  
  <p>Here's some snippets on my code:</p>
  
  <p>index.js:</p>
  
  <pre><code>ReactDOM.render(
    &lt;App /&gt;,
    document.getElementById('root')
  );
  </code></pre>
  
  <p>app.js (I hide all the obvious component imports):</p>
  
  <pre><code>import { BrowserRouter as Router, Route } from 'react-router-dom'
  
  class App extends Component {
    render() {
      return (
        &lt;Router&gt;
          &lt;div className="App"&gt;
            &lt;Route path='/'&gt;
              &lt;Header/&gt;
              &lt;div className="search-container"&gt;
                &lt;SearchBar/&gt;
                &lt;AddMovieButton/&gt;
              &lt;/div&gt;
              &lt;SearchResultsList/&gt;
            &lt;/Route&gt;
            &lt;Route exact path='/new'&gt;
              &lt;AddMovieForm/&gt;
            &lt;/Route&gt;
          &lt;/div&gt;
        &lt;/Router&gt;
      );
    }
  }
  
  export default App;
  </code></pre>
  
  <p>I can't really understand why this is not working, and why I have that error.</p>