title: void await function is preventing me from popping my second page. Says text field can't be null even when it's not null
body: <p>I'm passing text data from page 2 to page 1 like so:</p>
  <pre><code>  void _awaitReturnValueFromSecondScreen(BuildContext context) async {
      // start the SecondScreen and wait for it to finish with a result
      final result = await Navigator.push(
          context,
          MaterialPageRoute(
            builder: (context) =&gt; MakeCircle(),
          ));
      // after the SecondScreen result comes back update the Text widget with it
      setState(() {
        text = result;
      });
    }
  </code></pre>
  <p>This is my app bar item handler:</p>
  <pre><code>Future&lt;void&gt; handleClick(String value) async {
      switch (value) {
        case 'Circles':
          _awaitReturnValueFromSecondScreen(context);
          break;
  </code></pre>
  <p>The error pops up when I try exiting using the left arrow in the app bar.
  &quot;Failed Assertion. Data != null; a non-null String must be provided to a text widget.&quot;
  It exits fine when I use my floating button to exit... I want to be able to exit using the left arrow as well... Any ideas?</p>