ckeditorでfilebrowserからの画像のアップロードに失敗した時のメモ

こんなエラー

ActionController::RoutingError (No route matches [POST] "/ckeditor/EDITOR.config.filebrowserImageUploadUrl"):
  actionpack (4.1.0) lib/action_dispatch/middleware/debug_exceptions.rb:21:in `call'
  actionpack (4.1.0) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
  railties (4.1.0) lib/rails/rack/logger.rb:38:in `call_app'
  railties (4.1.0) lib/rails/rack/logger.rb:20:in `block in call'
  activesupport (4.1.0) lib/active_support/tagged_logging.rb:68:in `block in tagged'
  activesupport (4.1.0) lib/active_support/tagged_logging.rb:26:in `tagged'
  activesupport (4.1.0) lib/active_support/tagged_logging.rb:68:in `tagged'
  railties (4.1.0) lib/rails/rack/logger.rb:20:in `call'
  actionpack (4.1.0) lib/action_dispatch/middleware/request_id.rb:21:in `call'
  rack (1.5.2) lib/rack/methodoverride.rb:21:in `call'
  rack (1.5.2) lib/rack/runtime.rb:17:in `call'
  activesupport (4.1.0) lib/active_support/cache/strategy/local_cache_middleware.rb:26:in `call'
  rack (1.5.2) lib/rack/lock.rb:17:in `call'
  actionpack (4.1.0) lib/action_dispatch/middleware/static.rb:64:in `call'
  rack (1.5.2) lib/rack/sendfile.rb:112:in `call'
  railties (4.1.0) lib/rails/engine.rb:514:in `call'
  railties (4.1.0) lib/rails/application.rb:144:in `call'
  rack (1.5.2) lib/rack/lock.rb:17:in `call'
  rack (1.5.2) lib/rack/content_length.rb:14:in `call'
  rack (1.5.2) lib/rack/handler/webrick.rb:60:in `service'
  /Users/user/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
  /Users/user/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
  /Users/user/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'

Gemfileに以下を追加してbundle installで解決

gem 'activesupport-json_encoder', github: 'rails/activesupport-json_encoder'