Rails and Devise: undefined method `to' for nil:NilClass

Question

I would be immensely grateful for your help. I have begun setting up a rails app with devise and have had difficulty with my authentification. I have got to the point where I can create a new user and sign out, but I cannot login as a registered user. Currently, sign in attempt throws the error below. Signin is correctly going to the sessions#create controller, but the warden line is redirecting to failure app file on devise and throwing this error. Any help is greatly appreciated! For your information, I am also including my routes and SessionsController.

Image of Error on Signin Attempt

Devise routes in routes.rb

Devise SessionsController #new and #create