Rails 4: User Authentication - NoMethodError - ruby-on-rails

Question

I've setup a moreless simple social user authentification on top of devise using Google, Linkedin, Dropbox and Github.The Dropbox authentication does not work, instead it gives that error on the callback URL(http://localhost:3000/users/auth/dropbox/callback):
NoMethodError in Users::OmniauthCallbacksController#dropbox
undefined method `first' for nil:NilClass
Issue: User Model (line 8)
My Code:
Callbacks Controller:
class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
def all
user = User.from_omniauth(env['omniauth.auth'], current_user)
if user.persisted?
sign_in user
flash[:notice] = t('devise.omniauth_callbacks.success', :kind => User::SOCIALS[params[:action].to_sym])
if user.sign_in_count == 1
redirect_to edit_user_registration_path
else
redirect_to root_path
end
else
session['devise.user_attributes'] = user.attributes
redirect_to new_user_registration_url
end
end
User::SOCIALS.each do |k, _|
alias_method k, :all
end
end
User Model:
# omniauth Gem
def self.from_omniauth(auth, current_user)
authorization = Authorization.where(:provider => auth.provider, :uid => auth.uid.to_s,
:token => auth.credentials.token,
:secret => auth.credentials.secret).first_or_initialize
authorization.profile_page = auth.info.urls.first.last unless authorization.persisted?
if authorization.user.blank?
user = current_user.nil? ? User.where('email = ?', auth['info']['email']).first : current_user
if user.blank?
user = User.new
user.skip_confirmation!
user.password = Devise.friendly_token[0, 20]
user.fetch_details(auth)
user.save
end
authorization.user = user
authorization.save
end
authorization.user
end
def fetch_details(auth)
self.email = auth.info.email
self.username = auth.info.name
self.avatar = URI.parse(auth.info.image)
end
I appreciate each help! Thanks in advance.

Answer 1

To answer your question directly:
The undefined method "first" for nil::NilClass is happening because you are attempting to call the method first on an empty, or nil object.
It's probably in your user model where you are attempting to find a User from a current_user.
if authorization.user.blank?
user = current_user.nil? ? User.where('email = ?', auth['info']['email']).first : current_user
#This will cause the error that you are describing if both the current_user is nil and there is no User whose email is auth['info']['email']
Now, There's a few things wrong with this. If they are attempting to log in to your application, then current_user at this stage should be unset.
You could try changing this to
user = User.where(email: auth['info']['email']).first_or_create
Which will create a new instance of User, if one does not exist with the email provided in the Authorization.
Then you can continue with
user.persisted?
which returns true for an existing user, and false for a new instance of User