Set 'true' to: config.active_record.belongs_to_required_by_default

Author: yasulab

config/application.rb

@@ -36,7 +36,7 @@ class Application < Rails::Application
     # TODO: The following config should be switched to its default value `true`, but not urgent.
     # Rails 5.0: Require `belongs_to` associations by default. Previous versions had false.
     # https://railsguides.jp/configuring.html#config-active-record-belongs-to-required-by-default
-    config.active_record.belongs_to_required_by_default = false
+    config.active_record.belongs_to_required_by_default = true
 
     # Rails 8.0: `to_time` will always preserve the full timezone in Rails 8.1.
     config.active_support.to_time_preserves_timezone = :zone