Adobe Air: scroller throws error when changes focus between different applications

Question

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()
    at mx.core::UIComponent/setFocus()[E:\dev\4.y\frameworks\projects\framework\src\mx\core\UIComponent.as:9905]
    at spark.components::RichEditableText/setFocus()[E:\dev\4.y\frameworks\projects\spark\src\spark\components\RichEditableText.as:3126]
    at spark.components.supportClasses::SkinnableTextBase/setFocus()[E:\dev\4.y\frameworks\projects\spark\src\spark\components\supportClasses\SkinnableTextBase.as:1874]
    at mx.managers::FocusManager/activateWindowHandler()[E:\dev\4.y\frameworks\projects\framework\src\mx\managers\FocusManager.as:740]
    at flash.events::EventDispatcher/dispatchEventFunction()
    at flash.events::EventDispatcher/dispatchEvent()
    at mx.core::UIComponent/dispatchEvent()[E:\dev\4.y\frameworks\projects\framework\src\mx\core\UIComponent.as:13152]
    at spark.components::WindowedApplication/nativeWindow_activateHandler()[E:\dev\4.y\frameworks\projects\airspark\src\spark\components\WindowedApplication.as:2739]

In my Adobe Air program, I got the above error, whenever I use my app, and switch focus around between this app and other applications. (I've tried several times and this error is reproducible.)

What causes this problem and how to fix it?

EDIT: my program has a stackview, and one of the stackviews has a list. This error above will occur when the list has at least one object in.

Answer 1

I've got the same problem in one of my projects and looks like it's known bug of SDK. In my case I just wrote custom Scroller class where added focusManager != null check. Something like

package components
{
    import flash.events.FocusEvent;
    import spark.components.Scroller;
    public class MyScroller extends Scroller
    {
        public function MyScroller()
        {
            super();
        }

        override protected function focusInHandler(event:FocusEvent):void
        {
            if(focusManager != null) {
                super.focusInHandler(event);
            }
        }
    }
}

Best regrads, Roman