Fixed error causing missing sidebar after import

no issue
- the `Role.lowerCaseName` CP could throw an error when `name` was missing which caused the sidebar rendering to be aborted
- adds a guard to ensure we aren't calling string methods on `null` or `undefined`

ghost/admin/app/models/role.js

@@ -12,6 +12,6 @@ export default Model.extend({
     updatedBy: attr('number'),
 
     lowerCaseName: computed('name', function () {
-        return this.get('name').toLocaleLowerCase();
+        return (this.name || '').toLocaleLowerCase();
     })
 });