rails country select with state subregion in rails4

all. I'm following the carmen-rails documentation, though I'm using rails4, and I can't get the state subregion working when selecting a country. In fact, when leaving the subregion code in place I can't even navigate to the site. I get this error:

localhost:3000

Processing by OrdersController#new as HTML
  Rendered orders/_subregion_select.html.erb (1.9ms)
  Rendered orders/_form.html.erb (773.3ms)
  Rendered orders/new.html.erb within layouts/application (775.8ms)
Completed 500 Internal Server Error in 784ms

ActionView::Template::Error (undefined method `downcase' for nil:NilClass):
    1: <div id="order_state_wrapper">
    2:   <% parent_region ||= params[:parent_region] %>
    3:   <% country = Carmen::Country.coded(parent_region) %>
    4: 
    5:   <% if country.nil? %>
    6:     <em>Please select a country above</em>
  app/views/orders/_subregion_select.html.erb:3:in `_app_views_orders__subregion_select_html_erb__937058573181156642_69893053026600'
  app/views/orders/_form.html.erb:100:in `block in _app_views_orders__form_html_erb__3775537416523760398_69893046471120'
  app/views/orders/_form.html.erb:1:in `_app_views_orders__form_html_erb__3775537416523760398_69893046471120'
  app/views/orders/new.html.erb:6:in `_app_views_orders_new_html_erb__3931135682021831649_69893046299220'

Doesn't look like the (country, "US" in this case) paramater is being passed from the parent region because it's "nil". Any insight to get this working (I'm assuming with rails4) ?

app/views/orders/_form.html.erb

<div class="control-group">
  <div class="field">
    <%= f.label :country, 'Country' %>
    <%= f.country_select :country, priority: %w(US CA), prompt: 'Please select a country' %>
  </div>
  <div class="field">
    <%= f.label :state %><br />
    <%= render partial: 'subregion_select', locals: {parent_region: f.object.country} %>
  </div>
</div>

app/views/orders/_subregion_select.html.erb

<div id="order_state_wrapper">
  <% parent_region ||= params[:parent_region] %>
  <% country = Carmen::Country.coded(parent_region) %>
  <% if country.nil? %>
    <em>Please select a country above</em>
  <% elsif country.subregions? %>
    <%= subregion_select(:order, :state, parent_region) %>
  <% else %>
    <%= text_field(:order, :state) %>
  <% end %>
</div>

app/assets/javascripts/orders.js.coffee

# Place all the behaviors and hooks related to the matching controller here.
# All this logic will automatically be available in application.js.
# You can use CoffeeScript in this file: http://coffeescript.org/

$ ->
  $('select#order_country').change (event) ->
    select_wrapper = $('#order_state_wrapper')

    $('select', select_wrapper).attr('disabled', true)

    country = $(this).val()

    url = "/orders/subregion_options?parent_region=#{country}"
    select_wrapper.load(url)

config/routes.rb

get '/orders/subregion_options' => 'orders#subregion_options'

# rake routes

             Prefix      Verb   URI Pattern                          Controller#Action
orders_subregion_options GET    /orders/subregion_options(.:format)  orders#subregion_options

and when browsing to the subregion route directly and specifying a country:

http://localhost:3000/orders/subregion_options?parent_region=%22US%22

Started GET "/orders/subregion_options?parent_region=%22US%22" for 192.168.122.1 at 2013-07-08 13:20:21 -0400
Processing by OrdersController#subregion_options as HTML
  Parameters: {"parent_region"=>"\"US\""}
DEPRECATION WARNING: Relation#first with finder options is deprecated. Please build a scope and then call #first on it instead. (called from service at /usr/local/rvm/rubies/ruby-2.0.0-p195/lib/ruby/2.0.0/webrick/httpserver.rb:138)
  User Load (0.2ms)  SELECT "users".* FROM "users" WHERE "users"."id" = 1 ORDER BY "users"."id" ASC LIMIT 1
  Rendered orders/_subregion_select.html.erb (0.2ms)
Completed 200 OK in 4ms (Views: 1.3ms | ActiveRecord: 0.2ms)

Solution

The gem carmen-rails isn't registered on http://ready4rails4.net/, on the github page it written

carmen-rails is a Rails 3 plugin that supplies two new form helper methods: country_select and subregion_select.

plus on travis-ci.org https://travis-ci.org/jim/carmen-rails all builds are done with rails 3.2.

I would say the gem isn't Rails 4 ready maybe.

You should open an issue on the github page.

After having looked at your comment I have checked out the fork you're using and excepted the branch name I didn't saw any Rails 4 related commits.

Having a look at the changelog file (https://github.com/freerunningtechnologies/carmen-rails/blob/master/CHANGELOG.md) make me thinking that the rails 4 compatibility isn't done yet, but maybe I'm wrong.