NoMethodError (undefined method `relations' for nil:NilClass):

[yasirhashmi15]

I am trying to create new activity object as i followed below tutorial:

https://github.com/ging/social_stream/wiki/How-to-add-new-activity-objects

I created MVC using scaffold name subjects
I am receiving this error:

Started POST "/subjects" for 127.0.0.1 at 2014-06-17 15:00:06 +0100
Processing by SubjectsController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"dASWl4E7igoFk8UQdB9QUQw4ORq+xwdx2+aVzBYG0ho=", "subject"=>{"name"=>"test", "description"=>"test"}, "commit"=>"Create Subject"}
User Load (0.3ms) SELECT users.* FROM users WHERE users.id = 2 LIMIT 1
Actor Load (0.2ms) SELECT actors.* FROM actors WHERE actors.id = 2 LIMIT 1
ActivityObject Load (0.2ms) SELECT activity_objects.* FROM activity_objects WHERE activity_objects.id = 9 LIMIT 1
CACHE (0.0ms) SELECT actors.* FROM actors WHERE actors.id = 2 LIMIT 1
(0.2ms) BEGIN
(0.2ms) SELECT relations.id FROM relations INNER JOIN activity_object_audiences ON relations.id = activity_object_audiences.relation_id WHERE activity_object_audiences.activity_object_id IS NULL
(0.2ms) ROLLBACK
Completed 500 Internal Server Error in 104ms

NoMethodError (undefined method relations' for nil:NilClass): app/models/activity_object.rb:274:inallowed_relations'
app/controllers/subjects_controller.rb:47:in block in create' app/controllers/subjects_controller.rb:46:increate'

Rendered /Users/edudoc/.rvm/gems/ruby-1.9.3-p547/gems/actionpack-3.2.13/lib/action_dispatch/middleware/templates/rescues/_trace.erb (1.1ms)
Rendered /Users/edudoc/.rvm/gems/ruby-1.9.3-p547/gems/actionpack-3.2.13/lib/action_dispatch/middleware/templates/rescues/_request_and_response.erb (0.8ms)
Rendered /Users/edudoc/.rvm/gems/ruby-1.9.3-p547/gems/actionpack-3.2.13/lib/action_dispatch/middleware/templates/rescues/diagnostics.erb within rescues/layout (10.6ms)

Please help?

Thanks,
Yasir Hashmi