Fix sitemap nil

Fix namespace of role in subrole

lib/tasks/migrate.rake

@@ -307,7 +307,7 @@ namespace :migrate do
 
   task :sitemap_i18n => :environment do
     Item.all.each do |item|
-      item.sitemap_enabled = item.sitemap_enabled ? {'en' => 'true', 'zh_tw' => 'true'} : nil
+      item.sitemap_enabled = item.sitemap_enabled ? {'en' => 'true', 'zh_tw' => 'true'} : {}
       item.save
     end
   end