Followup of rails#18322

Mirror the documented new behavior of including details, when performing errors test.

activemodel/test/cases/errors_test.rb

@@ -11,7 +11,7 @@ def initialize
     attr_reader   :errors
 
     def validate!
-      errors.add(:name, "cannot be nil") if name == nil
+      errors.add(:name, :blank, message: "cannot be nil") if name == nil
     end
 
     def read_attribute_for_validation(attr)