title: Flutter: Fatal Error: Callback lookup failed! (with audioplayers package)
body: <p>The following snippet is the button by clicking which, a short beep plays:</p>
  
  <pre><code>FlatButton(
    onPressed: () =&gt; {
      final player = new AudioCache();
      player.play('note1.wav');
    }
    child: Text('Click to ding!'),
  ),
  </code></pre>
  
  <p>The problem I'm facing is whenever I click this button, although sound plays correctly, I get this error in terminal: <code>flutter: Fatal Error: Callback lookup failed!</code>
  I wanna know what it is and what I should do?</p>
  
  <p>I checked the <a href="https://github.com/luanpotter/audioplayers/issues/344" rel="noreferrer">package's issue page</a> but didn't find anything helpful.</p>
  
  <p>Thanks</p>