public_activity error

error_message.txt

Started GET "/activities" for 127.0.0.1 at 2015-02-24 09:32:47 +0200
Processing by ActivitiesController#index as HTML
  PublicActivity::Activity Load (0.5ms)  SELECT "activities".* FROM "activities"
  User Load (0.5ms)  SELECT  "users".* FROM "users"  WHERE "users"."id" = 3  ORDER BY "users"."id" ASC LIMIT 1
  Template Load (0.3ms)  SELECT  "templates".* FROM "templates"  WHERE "templates"."id" = $1 LIMIT 1  [["id", 11]]
  Rendered public_activity/template/_create.html.erb (1.5ms)
  User Load (0.4ms)  SELECT  "users".* FROM "users"  WHERE "users"."id" = $1 LIMIT 1  [["id", 3]]
  Template Load (0.3ms)  SELECT  "templates".* FROM "templates"  WHERE "templates"."id" = $1 LIMIT 1  [["id", 12]]
  Rendered public_activity/template/_create.html.erb (1.7ms)
  CACHE (0.0ms)  SELECT  "users".* FROM "users"  WHERE "users"."id" = $1 LIMIT 1  [["id", 3]]
  Template Load (0.3ms)  SELECT  "templates".* FROM "templates"  WHERE "templates"."id" = $1 LIMIT 1  [["id", 13]]
  Rendered public_activity/template/_create.html.erb (1.5ms)
  Order Load (0.4ms)  SELECT  "orders".* FROM "orders"  WHERE "orders"."id" = $1 LIMIT 1  [["id", 19]]
  Rendered public_activity/order/_create.html.erb (5.7ms)
  Rendered activities/index.html.erb within layouts/application (25.1ms)
Completed 500 Internal Server Error in 31ms

ActionView::Template::Error (undefined method `contacts' for #<Order:0x007fae732c8e08>):
    1: <% if activity.trackable %>new order is created
    2:   <%= link_to activity.trackable.contacts, activity.trackable %>
    3: <% else %>
    4:   order has since been removed
    5: <% end %>
  app/views/public_activity/order/_create.html.erb:2:in `_app_views_public_activity_order__create_html_erb___3808333553290960082_70193616701860'
  app/views/activities/index.html.erb:5:in `block in _app_views_activities_index_html_erb__3400982977608641421_70193616276800'
  app/views/activities/index.html.erb:2:in `_app_views_activities_index_html_erb__3400982977608641421_70193616276800'