Default Problem when trying to obtain a List from a Parcel object

Hi, I'm italian so I apologize for my bad english...

I have a problem when I use the method
Code:
readList(List outVal, ClassLoader loader)
I use this in this way
Code:
parcel.readList(mylist, null)
I want to put the list that I putted into the parcel object in mylist. But when I try to access to the list I obtain a nullPointerException...
What is wrong?