title: nested navigator pushedNamedAndRemoveUntil predicate route is null
body: <p>I'm trying to pushedNamedAndRemoveUntil but I'm noticing that my predicate keeps returning null as the route. </p>
  
  <p>My code:</p>
  
  <pre><code>Navigator.pushNamedAndRemoveUntil(
    context, 'search/studyPage',
    (Route&lt;dynamic&gt; route) {
      print(route);
      return false; // im returning false to illustrate that all the routes being "popped" are all returning null
      }, 
    arguments: StudyPageArgs(widget.study)
  );
  </code></pre>
  
  <p>This prints:</p>
  
  <pre><code>MaterialPageRoute&lt;dynamic&gt;(RouteSettings("null", null), 
  animation: AnimationController#117d7(⏭ 1.000; paused; 
  for MaterialPageRoute&lt;dynamic&gt;(null)))
  MaterialPageRoute&lt;dynamic&gt;(RouteSettings("null", null), 
  animation: AnimationController#117d7(⏭ 1.000; paused; 
  for MaterialPageRoute&lt;dynamic&gt;(null)))
  MaterialPageRoute&lt;dynamic&gt;(RouteSettings("null", null), 
  animation: AnimationController#117d7(⏭ 1.000; paused; 
  for MaterialPageRoute&lt;dynamic&gt;(null)))
  MaterialPageRoute&lt;dynamic&gt;(RouteSettings("null", null), 
  animation: AnimationController#117d7(⏭ 1.000; paused; 
  for MaterialPageRoute&lt;dynamic&gt;(null)))
  </code></pre>
  
  <p>When i do this, I am able to push to my previous route but popping from there just gives me a blank screen. It's because the predicate keeps returning null, so all previous routes are removed from the tree. Any idea what is happening?</p>
  
  <p>Please keep in mind that I am using a nested navigator set-up, identical to my other question here: (<a href="https://stackoverflow.com/questions/58574801/popuntil-with-nested-navigators">.popUntil with nested navigators</a>)</p>
  
  <p>Thanks</p>