创建Parse Role Hierarchy失败，'parent is undefined'

在Parse中设置角色层次结构时出现奇怪的错误:

Uncaught ReferenceError: parent is not defined

角色都是在Parse中创建的，我从getRoles中得到的关系对象看起来很好，但是当调用add方法时，我得到了这个错误。还有人有类似的经历吗?

function createRolesForOrganization(organization){
  var self = Parse.User.current();
  var ownerRole = new Parse.Role(organization.id + '_Owner', new Parse.ACL(self)),
      adminRole = new Parse.Role(organization.id + '_Admin', new Parse.ACL(self)),
      userRole = new Parse.Role(organization.id + '_User', new Parse.ACL(self));
  return Parse.Object
    .saveAll([
      ownerRole, 
      adminRole, 
      userRole
    ])
    .then(function(objs){
      ownerRole = objs[0];          
      adminRole = objs[1];
      userRole = objs[2];
      userRole.getRoles().add(adminRole);
      adminRole.getRoles().add(ownerRole);
      return Parse.Object.saveAll([
        ownerRole, 
        adminRole, 
        userRole
      ]);
    });
}