undefined method `_reference_instances'

[Nowaker]

>> ObjectSpace.each_object(ActiveRecord::Base).each do |obj|
?>   p Mass.references obj
>> end

NoMethodError: undefined method `_reference_instances' for #<Zone:0x00000002ab07c8>
        from /apps/zerigons/releases/4b3686948b8a29d68a4bf8647df55acc7c7d6f4b/vendor/bundle/ruby/1.9.1/bundler/gems/rails-3a3c18317943/activerecord/lib/active_record/attribute_methods.rb:275:in `method_missing'
        from /apps/zerigons/releases/4b3686948b8a29d68a4bf8647df55acc7c7d6f4b/vendor/bundle/ruby/1.9.1/gems/ruby-mass-0.1.3/lib/mass.rb:96:in `references'
        from (irb):9:in `block in irb_binding'
        from (irb):8:in `each_object'
        from (irb):8:in `each'
        from (irb):8
        from /opt/rbenv/versions/1.9.3-p484/bin/irb:12:in `<main>'