Rabl showing an empty json block

Rabl showing an empty json block

I am trying Rabl, however, I seem to receive a practically empty json block.
require_dependency "api/application_controller"
module Api
class RentablePropertiesController < ApplicationController
respond_to :json
def index
@r = Core::RentableProperty.all
# render :text => @r.to_json --> note: this renders the json correctly
render "api/rentable_properties/index" #note: rabl here does not
end
end
end
index.json.rabl collection @r
Output
[{"rentable_property":{}}]
Note: with a simply @r.to_json, it renders correctly:
[{"id":1,"description":"description","property_type_id":1,"created_at":"2013-08-22T19:04:35.000Z","updated_at":"2013-08-22T19:04:35.000Z","title":"Some
Title","rooms":null,"amount":2000.0,"tenure":null}]
Any idea why rabl doesn't work?