Not backwards compatible when adding new property using DataMember attribute

[crosscourt]

[DataMember(IsRequired = false)] public string NewField { get; set; }

It seems adding a new field is not supported. Got an exception "Input string was not in a correct format"

[yfakariya]

IsRequired of [DataMember] is not supported for backward compatibility methods now, you can get compatibility when you set SerializationMethod to Map instead of Array on SerializationContext.