title: React Rout v-4 `this.props.match.params` **undefined** and `staticContext` undefined
body: <p>I am using </p>
  
  <pre><code>    "react": "^15.6.1",
      "react-dom": "^15.6.1",
      "react-router": "^4.1.2",
  </code></pre>
  
  <p><strong>Hare my rout :</strong></p>
  
  <pre><code>&lt;BrowserRouter&gt;
          &lt;div&gt;
              &lt;Route exact path='/' component={Layout}&gt;&lt;/Route&gt;
              &lt;Route path='/about' name="about" component={About}&gt;
                  &lt;Route path="/:article" component={anotherAbout}&gt;&lt;/Route&gt;
              &lt;/Route&gt;
              &lt;Route path='/protfolio' name="protfolio" component={Portfolio}&gt;&lt;/Route&gt;
          &lt;/div&gt;
      &lt;/BrowserRouter &gt;
  </code></pre>
  
  <p>When i am call  <code>{this.props.match.params.article}</code> it give  <strong>undefined</strong></p>
  
  <p>And my Console: <code>this.props</code> 
  <a href="https://i.stack.imgur.com/vPBw9.png" rel="noreferrer"><img src="https://i.stack.imgur.com/vPBw9.png" alt="enter image description here"></a></p>
  
  <p>Why <code>staticContext: undefined</code> and my <code>props.match.params</code> null object.</p>