title: Cannot read property 'outlets' of null in Angular 4
body: <p>I have Angular 4.3.6 project where a template snippet produces this error.</p>
  
  <p>Template block:</p>
  
  <p><code>&lt;a [routerLink]="['/article',article?.id]"&gt;{{article?.title}}&lt;/a&gt;</code></p>
  
  <p>Error stack trace:</p>
  
  <pre><code>ArticleSpComponent.html:26 ERROR TypeError: Cannot read property 'outlets' of null
      at createNewSegmentGroup (router.es5.js:2967)
      at updateSegmentGroup (router.es5.js:2896)
      at router.es5.js:2914
      at forEach (router.es5.js:593)
      at updateSegmentGroupChildren (
  </code></pre>
  
  <p>The error cause seems to be obvious. article variable is fetched async from Http and initialized after page is rendered so firstly it's null. However I thought that putting ? after this variable allows to avoid this issue.</p>
  
  <p>Can you please advise?</p>