we don't need this

app/models/notification.rb

@@ -1,6 +1,6 @@
 class Notification < ActiveRecord::Base
   belongs_to :recipient, class_name: 'User'
-  belongs_to :target, :polymorphic => true
+  belongs_to :target, polymorphic: true
 
   class << self
     def for(recipient, options={})

app/models/notifications/question_answered.rb

@@ -1,5 +1,2 @@
 class Notifications::QuestionAnswered < Notification
-  def linked_object
-    Answer.where(id: self.target_id).first
-  end
 end