update

app/controllers/api/v1/rooms_controller.rb

@@ -1,6 +1,7 @@
 module Api
   module V1
     class RoomsController < Api::BaseController
+      load_resource :conference, find_by: :short_title
       respond_to :json
 
       def index
@@ -8,7 +9,7 @@ module Api
           rooms = Room.all
         else
           conference = Conference.find_by_guid(params[:conference_id])
-          rooms = conference.rooms
+          rooms = conference.venue.rooms if conference.venue
         end
         respond_with rooms
       end