ActionScript 3.0 :: Comparing Two Nested Objects?

So I am trying to populate a user state from XML in such a way that a new user will start with a set of default variables.

An example default state might be:

Code:
state={obj2:{foo:"bar"}};

This would then be changeable by the user so his foo could later be "bar2" and that would be saved to a database.

Now, let's say I want to add a new node to the xml, so the default would be:

Code:
default ={obj2:{foo:"bar", foo2:{foo:"bar"}}};

An earlier user would have no foo2, so an attempt to use state.obj2.foo2.foo on a text field would generate an error.

What I'd like to be able to do is see if state has a value and if not, fill the user's data with the matching node in the default (in pseudocode):

Code:
if (some function (state.obj2.foo2.foo ) is not there) {
// fill with default
state.obj2.foo2=default.obj2.foo2
}