【Flex】TypeError:无法访问空对象引用的属性或方法。

TypeError: Error #1009: 无法访问空对象引用的属性或方法。

at mx.managers::PopUpManagerImpl/addModalPopUpAccessibility()[E:\dev\4.y\frameworks\projects\framework\src\mx\managers\PopUpManagerImpl.as:1440]
at mx.managers::PopUpManagerImpl/modalPopUpCreationCompleteHandler()[E:\dev\4.y\frameworks\projects\framework\src\mx\managers\PopUpManagerImpl.as:1418]
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 mx.core::UIComponent/set initialized()[E:\dev\4.y\frameworks\projects\framework\src\mx\core\UIComponent.as:1818]
at mx.managers::LayoutManager/doPhasedInstantiation()[E:\dev\4.y\frameworks\projects\framework\src\mx\managers\LayoutManager.as:842]
at mx.managers::LayoutManager/doPhasedInstantiationCallback()[E:\dev\4.y\frameworks\projects\framework\src\mx\managers\LayoutManager.as:1180]错误出现行代码

http://www.68design.net/Web-Guide/Flash/41086-1.html