try to sign up, but can not

[ghost]

the apps works fine, but at time to sign up (i would like to try to use User.find(id).admin?, so i try to add a user and define it as admin one) i had an error:
"NoMethodError in Welcome#index
Showing /var/www/public_html/dummy/DummyApp/app/views/layouts/_current_user_info.html.haml where line #8 raised:
undefined method `name' for nil:NilClass"

after that, i will not be able to access root_path again (localhost:3000).