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] }