mongoid no method error

mongoid embedded documents error

NoMethodError in EventsController#update

undefined method `extract_id' for "test":String
Rails.root: /Users/yannick/Dropbox/projects/play/demo

Application Trace | Framework Trace | Full Trace
app/controllers/events_controller.rb:49:in `update'
Request

Parameters:

{"utf8"=>"✓",
 "_method"=>"put",
 "authenticity_token"=>"OYdrpsvPHL6633IJJGICkRKSvY1jSsv8IAYtJrg87iU=",
 "event"=>{"name"=>"Afro Cuban Lounge",
 "description"=>"big big party!!!",
 "venue_id"=>"4eb2fb49c25ed1214b000008",
 "date(1i)"=>"2011",
 "date(2i)"=>"11",
 "date(3i)"=>"3",
 "date(4i)"=>"09",
 "date(5i)"=>"40",
 "lessons"=>{"name"=>"test"}},
 "commit"=>"Save",
 "id"=>"afro-cuban-lounge"}