a missing sub document turns into a subdocument with undefined values, and schema validation fails - mongodb

Question

I have a schema.graphqls that looks like this:
type House {
id: ID!
rooms: Int!
address: String!
owner: Owner
}
type Owner: {
name: String!,
age: Int!
}
and a complementing mongoose schema:
export default class House {
static schema = {
rooms: Number
address: String,
owner: {
type : {
name: String,
age: Number
},
required: false
}
};
}
and I have an object in my mongodb looking like this (notice owner is missing intentionally):
ObjectId("xxx") {
rooms: 3,
address: "the street"
}
I'm trying to retrieve this document, the owner subdocument is missing (which is fine, its not mandatory).
The mongoose result fills this missing subdocument with undefined attributes,
ObjectId("xxx") {
rooms: 3,
address: "the street"
owner : {
name: undefined
age: undefined
}
which fails the schema validations (since indeed name and age are mandatory, if subdocument exists).
the actual error i'm getting is:
Resolve function for "House.owner" returned undefined
Could you possibly point me to whatever i'm doing wrong here?
thanks in advance

Answer 1

Following a direction from #Neil Lunn, I realised the problem is in the mongoose schema,
which led me to add required: false - which wasn't enough, but after adding also default: null voila.
problem solved. error gone.
final mongoose schema, to whom it may be of interest:
export default class House {
static schema = {
rooms: Number
address: String,
owner: {
type : {
name: String,
age: Number
},
required: false,
default: null
}
};
}