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
    );
  }
});