No such file to load -- map_fields in Rails 4.2

[rajosi]

I upgraded my Rails version from 3.2.13 to Rails 4.2.6. In the older version, they used map_fields plugin where in my contacts controller:

class ContactsController < ApplicationController
  require 'map_fields'
  map_fields :mapper, ['First Name','Last Name', 'Email', 'Notes'], :file_field => :file, :params => [:contact]

  def create
    @user = User.find(params[:user_id])
    @contact = @user.contacts.create(contact_params)
    respond_to do |format|
      if @contact.save
        format.json { render :json => { :notice => 'Contact was successfully created!',:redirect => user_contacts_url} }
        format.html { redirect_to(user_contacts_url(@user), :notice => 'Contact was successfully created!', :type => 'success') }
       else
        format.json { render :json => {:redirect => false} }
        format.html { render :action => "edit" }
      end
    end
  end
  def import
    @contact = Contact.new 
  end
    def mapper
    @contact = Contact.new(params[:contact])
    count = 0

    if fields_mapped?
      mapped_fields.each do |row|
        params[:contact] = {"user_id" => @current_user.id, "firstname" => row[0], "lastname" => row[1], "notes" => row[3], "email" => row[2].try(:strip)}
        contact = Contact.new(params[:contact])

        if contact.save
          count = count + 1
        end
      end

      if count > 0
        flash[:notice] = "#{count} Contact(s) created"
        redirect_to :action => :index
      else 
        flash[:notice] = "No contact was created..." 
        redirect_to :action => :index
      end

    else
      @best_row = @rows[1]
      render
    end

    rescue MapFields::InconsistentStateError
      flash[:error] = 'Please try again'
      redirect_to :action => :import
    rescue MapFields::MissingFileContentsError
      flash[:error] = 'Please upload a file'
      redirect_to :action => :import
  end

end

when I run the code I am getting the error

ActionController::RoutingError - undefined method write_inheritable_attribute' for ContactsController:Class: actionpack (4.2.6) lib/action_dispatch/routing/route_set.rb:63:inrescue in controller'
actionpack (4.2.6) lib/action_dispatch/routing/route_set.rb:58:in controller' actionpack (4.2.6) lib/action_dispatch/routing/route_set.rb:39:inserve'
actionpack (4.2.6) lib/action_dispatch/journey/router.rb:43:in block in serve' actionpack (4.2.6) lib/action_dispatch/journey/router.rb:30:inserve'
actionpack (4.2.6) lib/action_dispatch/routing/route_set.rb:817:in call' meta_request (0.4.0) lib/meta_request/middlewares/app_request_handler.rb:13:incall'
meta_request (0.4.0) lib/meta_request/middlewares/meta_request_handler.rb:13:in call' warden (1.2.6) lib/warden/manager.rb:35:inblock in call'
warden (1.2.6) lib/warden/manager.rb:34:in call' client_side_validations (4.2.5) lib/client_side_validations/middleware.rb:15:incall'
rack (1.6.4) lib/rack/etag.rb:24:in call' rack (1.6.4) lib/rack/conditionalget.rb:25:incall'
rack (1.6.4) lib/rack/head.rb:13:in call' remotipart (1.2.1) lib/remotipart/middleware.rb:27:incall'
actionpack (4.2.6) lib/action_dispatch/middleware/params_parser.rb:27:in call' actionpack (4.2.6) lib/action_dispatch/middleware/flash.rb:260:incall'
rack (1.6.4) lib/rack/session/abstract/id.rb:225:in context' rack (1.6.4) lib/rack/session/abstract/id.rb:220:incall'
actionpack (4.2.6) lib/action_dispatch/middleware/cookies.rb:560:in call' activerecord (4.2.6) lib/active_record/query_cache.rb:36:incall'
activerecord (4.2.6) lib/active_record/connection_adapters/abstract/connection_pool.rb:653:in call' actionpack (4.2.6) lib/action_dispatch/middleware/callbacks.rb:29:inblock in call'
activesupport (4.2.6) lib/active_support/callbacks.rb:88:in __run_callbacks__' activesupport (4.2.6) lib/active_support/callbacks.rb:778:in_run_call_callbacks'
activesupport (4.2.6) lib/active_support/callbacks.rb:81:in run_callbacks' actionpack (4.2.6) lib/action_dispatch/middleware/callbacks.rb:27:incall'
rails-dev-tweaks (1.2.0) lib/rails_dev_tweaks/granular_autoload/middleware.rb:36:in call' actionpack (4.2.6) lib/action_dispatch/middleware/remote_ip.rb:78:incall'
airbrake (4.3.8) lib/airbrake/rails/middleware.rb:13:in call' better_errors (2.1.1) lib/better_errors/middleware.rb:84:inprotected_app_call'
better_errors (2.1.1) lib/better_errors/middleware.rb:79:in better_errors_call' better_errors (2.1.1) lib/better_errors/middleware.rb:57:incall'
actionpack (4.2.6) lib/action_dispatch/middleware/debug_exceptions.rb:17:in call' rack-contrib (1.4.0) lib/rack/contrib/response_headers.rb:17:incall'
meta_request (0.4.0) lib/meta_request/middlewares/headers.rb:16:in call' actionpack (4.2.6) lib/action_dispatch/middleware/show_exceptions.rb:30:incall'
railties (4.2.6) lib/rails/rack/logger.rb:38:in call_app' railties (4.2.6) lib/rails/rack/logger.rb:20:inblock in call'
activesupport (4.2.6) lib/active_support/tagged_logging.rb:68:in block in tagged' activesupport (4.2.6) lib/active_support/tagged_logging.rb:26:intagged'
activesupport (4.2.6) lib/active_support/tagged_logging.rb:68:in tagged' railties (4.2.6) lib/rails/rack/logger.rb:20:incall'
actionpack (4.2.6) lib/action_dispatch/middleware/request_id.rb:21:in call' rack (1.6.4) lib/rack/methodoverride.rb:22:incall'
rack (1.6.4) lib/rack/runtime.rb:18:in call' activesupport (4.2.6) lib/active_support/cache/strategy/local_cache_middleware.rb:28:incall'
rack (1.6.4) lib/rack/lock.rb:17:in call' actionpack (4.2.6) lib/action_dispatch/middleware/static.rb:120:incall'
rack (1.6.4) lib/rack/sendfile.rb:113:in call' airbrake (4.3.8) lib/airbrake/user_informer.rb:16:in_call'
airbrake (4.3.8) lib/airbrake/user_informer.rb:12:in call' railties (4.2.6) lib/rails/engine.rb:518:incall'
railties (4.2.6) lib/rails/application.rb:165:in call' rack (1.6.4) lib/rack/content_length.rb:15:incall'
thin (1.5.1) lib/thin/connection.rb:81:in block in pre_process' thin (1.5.1) lib/thin/connection.rb:79:inpre_process'
thin (1.5.1) lib/thin/connection.rb:54:in process' thin (1.5.1) lib/thin/connection.rb:39:inreceive_data'
eventmachine (1.0.9.1) lib/eventmachine.rb:193:in run' thin (1.5.1) lib/thin/backends/base.rb:63:instart'
thin (1.5.1) lib/thin/server.rb:159:in start' rack (1.6.4) lib/rack/handler/thin.rb:19:inrun'
rack (1.6.4) lib/rack/server.rb:286:in start' railties (4.2.6) lib/rails/commands/server.rb:80:instart'
railties (4.2.6) lib/rails/commands/commands_tasks.rb:80:in block in server' railties (4.2.6) lib/rails/commands/commands_tasks.rb:75:inserver'
railties (4.2.6) lib/rails/commands/commands_tasks.rb:39:in run_command!' railties (4.2.6) lib/rails/commands.rb:17:in<top (required)>'
bin/rails:4:in `

'

This is my routes.rb file:

Htm::Application.routes.draw do
  .......................other routes......
  resources :contacts do
      post :import_remote,  :on => :collection
      get :import_remote,   :on => :collection
      collection  do
        post    :mapper
        get     :import
        post    :destroy_multiple
        delete  :destroy_all
      end
    end
end

I followed the same steps you given in issue 1, but I am getting this error. Please help.