前提・実現したいこと

Ruby on Ralisにて、Twitterログイン機能を作成しております。

発生している問題・エラーメッセージ

Twitterログインのボタンを押すと下記のメッセージが出るのですが、どのように対処するべきでしょうか？

Config>routes.rb

Rails.application.routes.draw do

  #devise_for :users ,controllers: { omniauth_callbacks: 'users/omniauth_callbacks' }
  #resources :photos
  root to: 'welcome#index'
  get '/auth/:provider/callback' => 'sessions#create'

end

app>users>sessions_controller.rb

class SessionsController < ApplicationController
  def create
   user = User.find_or_create_from_auth_hash(request.env['omniauth.auth'])
   session[:user_id] = user.id
   redirect_to root_path, notice: 'ログインしました'
  end
end

models>user.rb

class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable, :omniauthable

  def self.find_or_create_from_auth_hash(auth_hash)
    provider = auth_hash[:provider]
    uid = auth_hash[:uid]
    nickname = auth_hash[:info][:nickname]
    image_url = auth_hash[:info][:image]

    User.find_or_create_by(provider: provider, uid: uid) do |user|
      user.nickname = nickname
      user.image_url = image_url
    end
  end
end

  #def self.find_or_create_from_oauth(auth)
    # User.find_or_create_by(provider: auth.provider, uid: auth.uid) do |user|
     # user.user_name   = auth.info.nickname
     # user.avatar_url = auth.info.image
     # user.email      = User.dummy_email(auth)
     # user.password   = Devise.friendly_token[0, 20]
    # end
  # end

  # private

  #def self.dummy_email(auth)
   # "#{auth.uid}-#{auth.provider}@example.com"
  #end

db>migrate>20160125104011_devise_create_users.rb

class DeviseCreateUsers < ActiveRecord::Migration
  def change
    create_table(:users) do |t|
      ## Database authenticatable
      t.string :email,              null: false, default: ""
      t.string :encrypted_password, null: false, default: ""

      ## Recoverable
      t.string   :reset_password_token
      t.datetime :reset_password_sent_at

      ## Rememberable
      t.datetime :remember_created_at

      ## Trackable
      t.integer  :sign_in_count, default: 0, null: false
      t.datetime :current_sign_in_at
      t.datetime :last_sign_in_at
      t.string   :current_sign_in_ip
      t.string   :last_sign_in_ip

      ## Confirmable
      # t.string   :confirmation_token
      # t.datetime :confirmed_at
      # t.datetime :confirmation_sent_at
      # t.string   :unconfirmed_email # Only if using reconfirmable

      ## Lockable
      # t.integer  :failed_attempts, default: 0, null: false # Only if lock strategy is :failed_attempts
      # t.string   :unlock_token # Only if unlock strategy is :email or :both
      # t.datetime :locked_at


      t.timestamps null: false
    end

    add_index :users, :email,                unique: true
    add_index :users, :reset_password_token, unique: true
    # add_index :users, :confirmation_token,   unique: true
    # add_index :users, :unlock_token,         unique: true
  end
end

エラーメッセージ

https://gyazo.com/7aef0936833cd405feafcc16a2dc2b26

どうぞお願い致します。