Rails / Devise: undefined method `router_name' for nil:NilClass - what is coming through as nil?
<p>So this code (Devise &amp; OAuth2 in Rails 5)</p>

<pre><code>class Users::OmniauthCallbacksController &lt; Devise::OmniauthCallbacksController
    def google_oauth2
        puts request.env['omniauth.auth']
        @user = User.from_omniauth(request.env['omniauth.auth'])

        if @user.persisted?
            sign_in_and_redirect root_path, event: :authentication # &lt;--- THIS LINE IS THE CULPRIT
        else
            redirect_to root_path, flash: { error: 'Authentication failed!' }
        end
    end
end
</code></pre>

<p>tells me</p>

<pre><code>undefined method `router_name' for nil:NilClass
</code></pre>

<p>How do I go about tracking this down?</p>

<p>What exactly is it that is <strong>nil</strong> at this stage?</p>

<p>I got no enlightenment doing the following...</p>

<p><a href="https://i.stack.imgur.com/eHF93.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/eHF93.jpg" alt=""></a>
</p>

<p>and the server log...</p>

<pre><code>Started GET "/users/auth/google_oauth2" for ::1 at 2016-07-22 19:06:28 -0400
I, [2016-07-22T19:06:28.730884 #5714]  INFO -- omniauth: (google_oauth2) Request phase initiated.
Started GET "/users/auth/google_oauth2/callback?state=45315985daa3339fe9fa10f3e57dedaadfc4f4aa60f06f06&amp;code=4/I8O7qeJSR--qeDdep-Iwf1EkdI--SlAj2KWJz7MGCpE" for ::1 at 2016-07-22 19:06:34 -0400
I, [2016-07-22T19:06:34.760625 #5714]  INFO -- omniauth: (google_oauth2) Callback phase initiated.
Processing by Users::OmniauthCallbacksController#google_oauth2 as HTML
  Parameters: {"state"=&gt;"45315985daa3339fe9fa10f3e57dedaadfc4f4aa60f06f06", "code"=&gt;"4/I8O7qeJSR--qeDdep-Iwf1EkdI--SlAj2KWJz7MGCpE"}
  User Load (0.5ms)  SELECT  "users".* FROM "users" WHERE "users"."provider" = $1 AND "users"."uid" = $2 ORDER BY "users"."id" ASC LIMIT $3  [["provider", "google_oauth2"], ["uid", "106038339500381304171"], ["LIMIT", 1]]
Completed 500 Internal Server Error in 17ms (ActiveRecord: 4.5ms)



NoMethodError (undefined method `router_name' for nil:NilClass):

app/controllers/users/omniauth_callbacks_controller.rb:6:in `google_oauth2'
  Rendering /Users/davidwilbanks/.rvm/gems/ruby-2.3.1@global/gems/actionpack-5.0.0/lib/action_dispatch/middleware/templates/rescues/diagnostics.html.erb within rescues/layout
  Rendering /Users/davidwilbanks/.rvm/gems/ruby-2.3.1@global/gems/actionpack-5.0.0/lib/action_dispatch/middleware/templates/rescues/_source.html.erb
  Rendered /Users/davidwilbanks/.rvm/gems/ruby-2.3.1@global/gems/actionpack-5.0.0/lib/action_dispatch/middleware/templates/rescues/_source.html.erb (10.3ms)
  Rendering /Users/davidwilbanks/.rvm/gems/ruby-2.3.1@global/gems/actionpack-5.0.0/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb
  Rendered /Users/davidwilbanks/.rvm/gems/ruby-2.3.1@global/gems/actionpack-5.0.0/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb (2.1ms)
  Rendering /Users/davidwilbanks/.rvm/gems/ruby-2.3.1@global/gems/actionpack-5.0.0/lib/action_dispatch/middleware/templates/rescues/_request_and_response.html.erb
  Rendered /Users/davidwilbanks/.rvm/gems/ruby-2.3.1@global/gems/actionpack-5.0.0/lib/action_dispatch/middleware/templates/rescues/_request_and_response.html.erb (1.4ms)
  Rendered /Users/davidwilbanks/.rvm/gems/ruby-2.3.1@global/gems/actionpack-5.0.0/lib/action_dispatch/middleware/templates/rescues/diagnostics.html.erb within rescues/layout (98.5ms)
</code></pre>