Rails tutorial

When I was doing this exellent tutorial about rails, I got some problems the exercise 8.5 (ie : use session in place of cookies), the listing 9.6 doesn't work anymore. I had to search how to use session inside the utilities.rb file. Just replacing the word cookies by session does not work, got :

undefined method 'session' for nil:NilClass

The right code is here :

# Sign in when not using Capybara as well
post sessions_path, :session => { remember_token: user.remember_token }