What is this white box for?

My oppinion is that it has something to do with accoustics when closing the door, when i Hush Matted my doors (among other area) i took them off and didn't notice any difference. One might say that you don't need them after you insulate with proper insulation and remove the cellulose junk they use.

I have seen similar things in other doors. They seemed to just be a spacer so that there wasn't a big empty space there. No clue if that is what it is on the Versa though. Other cars something was needed there otherwise the plastic of the door panel would have alot of flex in it.

It's a stash box.