parolkar's pfeed plugin - problem while saving feeds

I have used parolker's pfeed plugin to log users activities but I am getting error while saving the feed. Below is the error message displayed.

TypeError (wrong argument type nil (expected Data)):
  /Users/me/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/syck.rb:401:in `emit'
  /Users/me/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/syck.rb:401:in `quick_emit'
  /Users/me/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/syck/rubytypes.rb:40:in `to_yaml'
  vendor/plugins/pfeed/app/models/pfeed_item.rb:37:in `log'
  (eval):7:in `start_followup_with_pfeed'
  app/controllers/individuals_controller.rb:329:in `add_followup'
  /Users/me/.rvm/gems/ruby-1.9.2-p180@suga/gems/hoptoad_notifier-2.4.9/lib/hoptoad_notifier/rack.rb:27:in `call'
  /Users/me/.rvm/gems/ruby-1.9.2-p180@suga/gems/hoptoad_notifier-2.4.9/lib/hoptoad_notifier/user_informer.rb:12:in `call'
  :10:in `synchronize'
  /Users/me/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/webrick/httpserver.rb:111:in `service'
  /Users/me/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/webrick/httpserver.rb:70:in `run'
  /Users/me/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/webrick/server.rb:183:in `block in start_thread'

The开发者_如何学Python error message points line 37 of pfeed_item.rb which is p_item.save! I tried p_item.errors but it returns empty message.

Do you guys have any idea?

Thanks in advance :)

PS: Rails 2.3.5 and Ruby 1.9.2-p180

=========

Model: individual.rb

def start_followup(ind_followup)
  puts "added follow-up"
end

def complete_followup(ind_followup)
  puts "completed follow-up"
end

emits_pfeeds :on => [:start_followup,:complete_followup] , :for => [:itself]   # Note: if feed needs to be received by all users , you could use :for => [:all_in_its_class]
receives_pfeed

The model method is called from controller as

@individual.start_followup(@followup)

Beside this everything is done in pfeeds.