IgnoreIfDefault on Immutable Value Object in Dotnet Core

Hi Team, I want to use [IgnoreIfNull] on Immutable Value Objects. Can you guide me for implementation for the same? Below is example:

Class Definition:

public class User
{
[IgnoreIfNull] // This is working well
public string? Id{get;set;}
[IgnoreIfNull] //This is also working when FirstName and Last Name are null, but not working when FirstName is not null but LastName is null.
public Names FullName{get;set;}
}

Value Object:

public record class Names(string? FirstName, string? LastName)
{
public Names():this(null, null)
{
}
}