ActionScript 3.0 :: Finding Masks In MovieClips?

I'm trying "get" the masked objects in my MovieClip object using something like:

ActionScript Code:
for(var i:uint=0; i<myMC.numChildren; i++){
if(myMC.getChildAt(i).mask!=null){
maskedObject = myMC.getChildAt(i);
break;
}
}

It goes through myMC's children and never finds a masked object even though myMC does have a mask in it. I made myMC in flash, so is that the problem? And how would i access the masked object otherwise?