Subpermissions sent to back-end should be strings only

PUT /perms/permissions/f2808d5e-5ba6-4c3f-aa07-3c8eaf351059
{
   "visible" : true,
   "subPermissions" : [
      {
         "subPermissions" : [
            "circulation.loans.collection.get",
            "circulation.loans.item.get",
            "circulation.loans.item.post",
            "circulation.loans.item.put",
            "circulation.loans.item.delete",
            "circulation.loans.collection.delete"
         ],
         "visible" : false,
         "permissionName" : "circulation.all",
         "description" : "Entire set of permissions needed to use the circulation module",
         "tags" : [],
         "id" : "437a9009-15f6-4b5b-8fd9-dcbacf850272",
         "mutable" : false,
         "displayName" : "circulation module - all permissions"
      }
   ],
   "permissionName" : "f2808d5e-5ba6-4c3f-aa07-3c8eaf351059",
   "tags" : [],
   "id" : "f2808d5e-5ba6-4c3f-aa07-3c8eaf351059",
   "mutable" : true,
   "description" : "Just for testing",
   "displayName" : "Mike's set"
}

PUT /perms/permissions/f2808d5e-5ba6-4c3f-aa07-3c8eaf351059
{
   "visible" : true,
   "subPermissions" : [ "circulation.all" ],
   "permissionName" : "f2808d5e-5ba6-4c3f-aa07-3c8eaf351059",
   "tags" : [],
   "id" : "f2808d5e-5ba6-4c3f-aa07-3c8eaf351059",
   "mutable" : true,
   "description" : "Just for testing",
   "displayName" : "Mike's set"
}