title: Return action when the result is an empty array
body: <p>It is possible to make this to return an action (fulfilled) when the first <code>mergeMap</code> returns an empty array?</p>
  <pre class="lang-js prettyprint-override"><code>of(1)
      .pipe(
        mergeMap(x =&gt; []), // this can result in empty array
        distinct(),
        mergeMap(x =&gt; {
          ...
          return fulfilled()
        })
      )
      .subscribe((x) =&gt; console.log(x));
  </code></pre>