Menu editor fails when all menu items have been deleted

The menu editor fails when all menu items are deleted.

Steps to reproduce:
1. login to a CMS
2. edit a channel
3. edit a menu of the channel via the 'Edit Menu' button
4. delete each top-level menu item

Expected: after the last menu item has been deleted, the editor shows something like "no menu items" and provides a way to add the first menu item to the menu

Actual: the menu editor shows an empty tree area and the last item that was deleted on the right-hand side. It also logs the following JavaScript errors:

Error: Could not resolve 'menu-item.add' from state 'menu-item.edit'
at Object.u.transitionTo (angular-ui-router.min.e970bf8b.js:7)
at Object.u.go (angular-ui-router.min.e970bf8b.js:7)
at EditMenuItemCtrl.4382c1d5.js:200
at angular.js:12901
at h.$get.h.$eval (angular.js:14110)
at h.$get.h.$digest (angular.js:13926)
at h.$get.h.$apply (angular.js:14214)
at n (angular.js:9474)
at O (angular.js:9659)
at XMLHttpRequest.D.onload (angular.js:9602)
angular.js:11339 TypeError: Cannot read property '$$hashKey' of undefined
at Object.F [as extend] (angular.js:423)
at MenuItemCtrl.f13a2a6e.js:49
at angular.js:12901
at h.$get.h.$eval (angular.js:14110)
at h.$get.h.$digest (angular.js:13926)
at h.$get.h.$apply (angular.js:14214)
at n (angular.js:9474)
at O (angular.js:9659)
at XMLHttpRequest.D.onload (angular.js:9602)