Flarum\Admin\AdminServiceProvider::register PHP Method

    public function register()
    {
        $this->app->singleton(UrlGenerator::class, function () {
            return new UrlGenerator($this->app, $this->app->make('flarum.admin.routes'));
        });
        $this->app->singleton('flarum.admin.routes', function () {
            return new RouteCollection();
        });
    }