title: Angular RxJS: Subject<void>.asObservable() returns undefined
body: <p>I've created an <code>Subject</code> in order to populate some event clicks:</p>
  
  <pre><code>&lt;button type="search" class="btn btn-primary" (click)="search()"&gt;
      &lt;i class="fa fa-search" aria-hidden="true"&gt;&lt;/i&gt; Cercar
  &lt;/button&gt;
  </code></pre>
  
  <p>My component is:</p>
  
  <pre><code>private searchClickSubject:Subject&lt;void&gt;;
  private searchClick$:Observable&lt;void&gt;;
  
  constructor() {
      this.searchClickSubject = new Subject&lt;void&gt;();
      this.searchClick$ = this.searchClickSubject.asObservable();   &lt;&lt;&lt;1&gt;&gt;&gt;
  }
  
  private search(): void {
      this.searchClickSubject.next();
  }
  </code></pre>
  
  <p>Nevertheless, after <code>&lt;&lt;&lt;1&gt;&gt;&gt;</code>, <code>this.searchClick$ = this.searchClickSubject.asObservable();</code>, it returns <code>undefined</code>.</p>
  
  <p>Any ideas?</p>