Persist Facebook profile picture url on Rails 3

I added Facebook Authentication to my Rails 3 app according to this tutorial and it works great.

Now I want to display the username and profile picture as soon as he / she is logged into the app using Facebook. I've tried following the solution given here: Rails: Retrieving Image from Facebook after Logging in to Omniauth with Devise

But then I get the following error:

"Unable to assign protected attributes: name, image"

Any ideas on how I can get this to work?