title: error in passing arguments and list duplicating passed items two times in flutter
body: <p>I am using <code>arguments</code> method in <code>Navigator</code> to pass a List</p>
  <pre><code>Navigator.pushNamed(context, '/cam', arguments: {'label' : list});
  </code></pre>
  <p><code>list</code> is a string of items separated by comma for eg: <code>item1, item2</code></p>
  <p>and on receiving the the map of data from the first screen in second screen, I store that in a List by</p>
  <pre><code>data = ModalRoute.of(context).settings.arguments;
  print(data);
  rekognition.add(data['label']);
  print(rekognition);
  </code></pre>
  <p>under Widget build and the above print statements prints <code>[null, item1, item2</code>] and <code>[null, item1, item2, null, item1, item2]</code> respectively.</p>
  <p>this is where the problem is I don't why <code>null</code> pop up here and the list adds all the items second time</p>
  <p>also</p>
  <pre><code>for (x=0; x&lt;ing.length; x++) {
      list = '$list , ${ing[x]}';
  }
  </code></pre>
  <p><code>ing</code> is again a list and its equal to <code>List&lt;dynamic&gt;();</code></p>
  <p>all I wanted to do was send a list of items which is added in the first screen and or else a empty list to the second screen and add all those received data to another variable in second screen and do object detection and add the label to the list of items that was passed form the first screen and go back to the first screen again with data of the all the list items including the data that was passed and added</p>