NoMethodError in Classified#create nil object

As a matter a fact, the error is related to the validation itself. It
'crashes' on the relation category-classified.
So far I found out that the error is introduced in chapter 5 after
adding the relation category-classified. It has nothing to do with file
upload.
If you remove the validations from the model it all works fine.

So far, the author hasn't come back with an answer to fix it.
Ideally, you should be able to trap the errors

Anybody got an idea how to overcome this? APparantly, the Ruby code
tries to retrieve associated records from a category, without having an
instantiated classifieds array.

Hi, finally I found the solution for this problem, as Marcel Dohmen
said, the validation crashes on relation category-classified, defined
on classified.rb. just change "belongs_to :category", after all the
validations.

I hope it works to you.

PD: Sorry about my english,