Dotnet nullable types not compatible with graphql – GraphQL

I’m migrating from the Realm Cloud.

If I define nullable types in the dotnet RealmObject

public double? A { get; set; }

and save it as null
the document saved in mongodb will be like

{
…
A: null
…
}

and the following error will occur when querying in graphql interface

1. message: “reason=“could not validate document: ntA: Invalid type. Expected: undefined, given: null”; code=“SchemaValidationFailedRead”; untrusted=“read not permitted”; details=map[]”

Anyone can help? Thanks a lot!