problems select list generated from tables

I would like to generate a select list form multiple associations and
I'm not being able to. Do not know what the problem is. Hope anyone can
help.

the code below gives me a: "You have a nil object when you didn't
expect it!
The error occurred while evaluating nil.filename"

@skinType = Furni.find(:all, :include =>[:imageasset => {:skin =>
[:skintype, :skinstyle]}]).map {|st| [st.imageasset. filename, st.id] }