public function getNavigation()
    {
        /** @var Navigation $navigation */
        $navigation = null;
        $this->iterateAdmins(function(Admin $admin) use (&$navigation) {
            if (null === $navigation) {
                $navigation = $admin->getNavigation();

                return;
            }
            $navigation = $navigation->merge($admin->getNavigation());
        });

        return $navigation;
    }