ServiceStack Deserializing Interface property null in object

I want to use ServiceStack JsonSerializer.

I am setting IncludeTypeInfo property true before I serialize my object.And my serialized string contains all type informations like "__type":".Interfacesb,....

When I want to deserialize string that time my interface property null even though I have type information in my serialized string.Is there any other configuration need when deserializing object.

I use two methods JsonSerializer.SerializeToString and JsonSerializer.DeSerializeFromString

Example:

JsConfig.IncludeTypeInfo = true;

Public Class MyObject
{
Public string a{get;set;}
Public interface  b{get;Set;}
}