app/models/mailkick/opt_out.rb in mailkick-0.2.0 vs app/models/mailkick/opt_out.rb in mailkick-0.2.1

@@ -1,7 +1,7 @@
 module Mailkick
   class OptOut < ActiveRecord::Base
     self.table_name = "mailkick_opt_outs"
 
-    belongs_to :user, polymorphic: true
+    belongs_to :user, ActiveRecord::VERSION::MAJOR >= 5 ? {polymorphic: true, optional: true} : {polymorphic: true}
   end
 end