diff --git a/lib/devise/controllers/sign_in_out.rb b/lib/devise/controllers/sign_in_out.rb
index 526b41ea..6d72a21d 100644
--- a/lib/devise/controllers/sign_in_out.rb
+++ b/lib/devise/controllers/sign_in_out.rb
@@ -106,10 +106,12 @@ module Devise
       private
 
       def expire_data_after_sign_in!
+        # TODO: remove once Rails 5.2+ and forward are only supported.
         # session.keys will return an empty array if the session is not yet loaded.
         # This is a bug in both Rack and Rails.
         # A call to #empty? forces the session to be loaded.
         session.empty?
+
         session.keys.grep(/^devise\./).each { |k| session.delete(k) }
       end