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.