title: Focus Manager bug in Scroller class
body: <p>In the Scroller.as class line 2139 I'm getting the following error:</p>
  
  <pre><code>TypeError: Error #1009: Cannot access a property or method of a null object reference.
      at spark.components::Scroller/focusInHandler()[E:\dev\4.y\frameworks\projects\spark\src\spark\components\Scroller.as:2139]
      at flash.display::Stage/set focus()
  </code></pre>
  
  <p>From Scroller.as</p>
  
  <pre><code>/**
   *  @private 
   *  Listens for any focusIn events from descendants 
   */ 
  override protected function focusInHandler(event:FocusEvent):void
  {
      super.focusInHandler(event);
  
      // When we gain focus, make sure the focused element is visible
      if (viewport &amp;&amp; ensureElementIsVisibleForSoftKeyboard)
      {
          var elt:IVisualElement = focusManager.getFocus() as IVisualElement; 
          lastFocusedElement = elt;
      }
  }
  </code></pre>
  
  <p>Since this is framework code what option do I have to prevent it? </p>
  
  <p><strong>Context</strong><br>
  I have created a pop up TitleWindow, added a Module in it and displayed it. The Module has a few States, in each State is a Group, one Group has a List, that List has an ItemRenderer, that ItemRenderer has a Checkbox. </p>
  
  <p>The Module also has a Menu. When the Menu is opened the menu pop up lists the states the Module has available. When an item is selected from the menu pop up I change to another state. </p>
  
  <p>When the state is changed and the last item is the checkbox then the error is generated. At least that's what I think is happening. I deduced this because in the Scroller class the handler is handling an event. On that event is the current target. That current target is the checkbox. </p>
  
  <p><strong>Update</strong> - Steps to reproduce</p>
  
  <pre><code>// inside the Application.mxml
  // define variables
  public var popup:Group;
  public var titleWindow:TitleWindow;
  
  
  // shows pop up
  public function showInspector():void {
  
      // inside show inspector method
      // create new inspector container
      popup = new InspectorContainer(); // a group implements="mx.managers.IFocusManagerContainer"
      titleWindow = new TitleWindow();
      titleWindow.addElement(popup);
  
      // display pop up title window
      PopUpManager.addPopUp(titleWindow, this, false);
  }
  
  &lt;fx:Declarations&gt;
      &lt;modules:InspectorContainer/&gt;
  &lt;/fx:Declarations&gt;
  </code></pre>
  
  <ol>
  <li><p>Show pop up. The pop up is a Title Window with InspectorContainer (a group) as the first element.</p></li>
  <li><p>In pop up change from home state (default state) to online state (this happens when the user clicks a button). The online state has a List. The List has an itemrenderer. The itemrenderer has a checkbox. Select the checkbox. So far so good.</p></li>
  <li><p>The pop up (InspectorContainer) has a mx:MenuBar instance. When you click on an item in the menubar the menubar displays a menu items. </p></li>
  <li><p>Click an item in the menu list. The itemClick menuHandler is called. In this function the pop up changes state. </p></li>
  </ol>
  
  <p>This is when the error occurs. </p>