hitTestObject problem.

[bobet]

I am converting a as2 file to as3. I am trying to convert this. I tried this:

for (var a:uint=1; a<=10; a++) {
if (player.hitTestObject(root.["wall"+a]) == true) {
player.x += 0;
}
}

but i get this error.
TypeError: Error #2007: Parameter hitTestObject must be non-null.
at flash.display:isplayObject/flash.displayisplayObject::_hitTest()
at flash.display:isplayObject/hitTestObject()
at MyFile_fla::MainTimeline/onEnterFrame()