null pointer exception in PopUpManagerImpl

take a look on line 780, PopUpManagerImpl.as, the code try to access "visible" property without testing if "popup" if not null. (which is done properly a few lines before to add event listeners)

if (visibleFlag)
showModalWindow(o, sm, false);
else
popup.visible = visibleFlag; // BANG, null pointer exception

I found this bug loading flex 4 SWF inside a AIR app with SWFLoader.