title: startWith value is null the first time, even with non null first selection. why?
body: <p>I have a group dropdown, and when selecting from the drop down the first time, the startWith value is always null. Why is this happening? In subsequent selection from dropdown, startWith() gets the right value.</p>
  <p>So selecting from dropdown drives this list.</p>
  <p>My template looks something like this:</p>
  <pre><code>&lt;person-list
      [list]=list$
  &lt;/person-list&gt;
  </code></pre>
  <p>My component class</p>
  <pre><code>ngOnInit() {
      list$ = this.getNames();
  }
  
  getNames():Observable&lt;Name[]&gt; {
  
      return formControl.valueChanges.pipe(
      startWith(formControl.value),
      switchMap(group =&gt; {
         return http.getNames();
      })
   )}
  </code></pre>