default value for disabled_oauth_sign_in_sources in create_from_defaults @ ApplicationSetting

app/models/application_setting.rb

@@ -157,6 +157,7 @@ class ApplicationSetting < ActiveRecord::Base
       recaptcha_enabled: false,
       akismet_enabled: false,
       repository_checks_enabled: true,
+      disabled_oauth_sign_in_sources: []
     )
   end