Revert "Merge pull request rails#13276 from aayushkhandelwal11/change_to_key"

This will call primary_key two times

This reverts commit d0588a2, reversing
changes made to 87e1e86.

Author: rafaelfranca

activemodel/lib/active_model/conversion.rb

@@ -49,7 +49,8 @@ def to_model
     #   person = Person.create
     #   person.to_key # => [1]
     def to_key
-      [id] if respond_to?(:id) && id
+      key = respond_to?(:id) && id
+      key ? [key] : nil
     end
 
     # Returns a +string+ representing the object's key suitable for use in URLs,