Error when setting field as null in Mongoose - node.js

Question

I am using MongooseJS. I am getting the error below:
{ message: 'Cast to ObjectId failed for value "" at path "parent"',
name: 'CastError',
type: 'ObjectId',
value: '',
path: 'parent'
}
I don't want to set a parent for this object. Where am I wrong? What should I do?
Update:
var category = new Category(req.body)
if(typeof category.parent === 'undefined'){
category.parent=undefined;
}
And the category schema is:
var CategorySchema = new Schema({
name: {
tr: {type : String, default : '', trim : true},
en: {type : String, default : '', trim : true}
},
description: {
tr: {type : String, default : '', trim : true},
en: {type : String, default : '', trim : true}
},
subcategories:[{type : Schema.ObjectId, ref : 'Category', null: true}],
parent: {type : Schema.ObjectId, ref : 'Category', null: true},
products:[{type : Schema.ObjectId, ref : 'Product'}],
images : [String],
order: {type : Number, default: 0},
createdAt : {type : Date, default : Date.now},
locale: {type : String, null: false}
})
My jade code is:
.controls
select#parent(name="parent")
option(value="") Select
each cat in categories
- if (category.subcategories.map(function(e) { return e.id; }).indexOf(cat.id) != -1)
option(value=cat.id, selected) #{cat.name.tr}
- else
option(value=cat.id) #{cat.name.tr}
So if user do not select a parent, it sends "" to server and server gives that error.

Answer 1

The error states you can't cast the type you're trying to set into the category.parent property as it's expecting an ObjectId. I'd expect that the parent field value coming through req.body is not an ObjectId
Also, all properties are defined on a MongooseJs model and won't be undefined.
You need to set it to null:
category.parent = null;
This will clear the value.

Answer 2

Old question, but I got the same issue and want to share the answer. Before creating the Category-Object you have to manually delete the parent-property from req.body, if it's not setted with a valid value:
if (req.body.parent == "")
delete req.body.parent; // or req.body.parent = null;
var category = new Category(req.body);
Setting it afterwards to null won't work - don't ask me why.