discourse/app/assets/javascripts/admin/routes/admin-site-settings-index.js.es6

/**
  Handles when you click the Site Settings tab in admin, but haven't
  chosen a category. It will redirect to the first category.
**/
export default Discourse.Route.extend({
  beforeModel() {
    this.replaceWith('adminSiteSettingsCategory', this.modelFor('adminSiteSettings')[0].nameKey);
  }
});