empty_model.to_xml with attr_accessor attributes?

Hello there,

I have an empty Asset model which only contains 3 attr_accessor
attributes (:uploaded_data, :title, :description), which I can fill
just fine using form_for etc, but when trying to do it restfully, the /
assets/new.xml just returns an empty

<?xml version="1.0" encoding="UTF-8"?>
<asset>
</asset>

Is there a way to serialize / @asset.to_xml including the
uploaded_data/title/description attributes?

format.xml { render :xml => @asset.to_xml(:only =>
[:uploaded_data, :title, :description]) } returns the same as
above... :-/

Thanks,
-Jörg