我正在尝试动态地向舞台添加一个List对象，但是在调用某一行时总是会出错：
input.addItem({label:"test",data:"test"});
运行时抛出错误：
TypeError: Error #2007: Parameter child must be non-null.
at flash.display::DisplayObjectContainer/addChildAt()
at fl.controls::BaseButton/fl.controls:BaseButton::drawBackground()
at fl.controls::LabelButton/fl.controls:LabelButton::draw()
at fl.core::UIComponent/drawNow()
at fl.controls::List/fl.controls:List::drawList()
at fl.controls::List/fl.controls:List::draw()
at fl.core::UIComponent/fl.core:UIComponent::callLaterDispatcher()
TypeError: Error #2007: Parameter child must be non-null.
at flash.display::DisplayObjectContainer/addChildAt()
at fl.controls::BaseButton/fl.controls:BaseButton::drawBackground()
at fl.controls::LabelButton/fl.controls:LabelButton::draw()
at fl.core::UIComponent/fl.core:UIComponent::callLaterDispatcher()
有人有任何想法如何解决这个问题？谢谢你的帮助。