Unable to add custom fields to my Devise user model in Rails 4 with strong parameters

I've tried everything I can find, including what is in the Devise README (https://github.com/plataformatec/devise#strong-parameters), this more descriptive take on the README (http://blog.12spokes.com/web-design-development/adding-custom-fields-to-your-devise-user-model-in-rails-4/comment-page-1/#comment-26217), and every answer I find on StackOverflow seems consistent with these 2 solutions. All these solutions result in the same error: 2 errors prohibited this user from being saved: - Email can't be blank - Password can't be blank

I also tried including gem 'protected_attributes' in the gemfile and running bundle so that I could use attr_accessible rather than strong parameters. With this approach, it appeared that I was able to save the user okay, but none of my fields, custom or otherwise, actually persisted. They all remained nil. I also tried reverting devise back to a previous version where attr_accessible was used rather than strong parameters and that resulted in the same issue where nothing persisted.

I'm at a complete standstill with this at the moment so any ideas on other solutions that may work would be greatly appreciated... Thanks in advance!

EDIT: Here's my application controller:

class ApplicationController < ActionController::Base
  before_filter :configure_permitted_parameters, if: :devise_controller?

  protected

  def configure_permitted_parameters
         devise_parameter_sanitizer.for(:sign_in) { |u| u.permit(:profile_name, :email, :password) }
         devise_parameter_sanitizer.for(:sign_up) { |u| u.permit(:first_name, :last_name, :profile_name, :email, :password, :password_confirmation) }
         devise_parameter_sanitizer.for(:account_update) { |u| u.permit(:first_name, :last_name, :profile_name, :email, :password, :password_confirmation, :current_password) }
  end


  # Prevent CSRF attacks by raising an exception.
  # For APIs, you may want to use :null_session instead.
  protect_from_forgery with: :exception

end

I have created an sample app and this works for me.

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
end

in devise registrations new.html.erb view

<%= form_for(resource, :as => resource_name, :url => registration_path(resource_name)) do |f| %>
  <%= devise_error_messages! %>

  <div><%= f.label :firstname %><br />
  <%= f.text_field :firstname, :autofocus => true %></div>

  <div><%= f.label :lastname %><br />
  <%= f.text_field :lastname %></div>

  <div><%= f.label :email %><br />
  <%= f.email_field :email, :autofocus => true %></div>

  <div><%= f.label :password %><br />
  <%= f.password_field :password %></div>

  <div><%= f.label :password_confirmation %><br />
  <%= f.password_field :password_confirmation %></div>

  <div><%= f.submit "Sign up" %></div>
<% end %>

<%= render "devise/shared/links" %>

and in devise_create_user migration

class DeviseCreateUsers < ActiveRecord::Migration
  def change
    create_table(:users) do |t|
      ## Database authenticatable
      t.string :firstname
      t.string :lastname
      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.string :authentication_token


      t.timestamps
    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

in routes

Topic::Application.routes.draw do

  devise_for :users#, controllers: { registrations: "registrations" }

  resources :maintopics do
    resources :subtopics
  end
end

and in application controller

class ApplicationController < ActionController::Base
  # Prevent CSRF attacks by raising an exception.
  # For APIs, you may want to use :null_session instead.

  before_filter :configure_permitted_parameters, if: :devise_controller?

  def configure_permitted_parameters
   devise_parameter_sanitizer.for(:sign_up) { |u| u.permit(:firstname, :lastname, :email, :password, :password_confirmation) }
  end

  protect_from_forgery with: :exception

end

In your case i think there is an problem of parameters so create new registration controller and add following code in it to check the parameters value.

class RegistrationsController < Devise::RegistrationsController

  def create
    raise params.inspect
  end
end

in routes file replace existing with following line.

devise_for :users, controllers: { registrations: "registrations" }