http://railscasts.com/episodes/235-omniauth-part-1およびhttp://railscasts.com/episodes/236-omniauth-part-2のチュートリアルに従いましたが、エラーが発生します
You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.[]
私は何をすべきか?
更新:エラー
app/models/user.rb:9:in `apply_omniauth'
app/controllers/authentications_controller.rb:18:in `create'