When handling message that uses a base type, messages are null

[bibodha]

public class MySaga : IStatefulSaga
{
    public void Orchastrates(EventBaseType typeA)
    {

    }
    public void Orchastrates(EventUsingType typeB)
    {

    }    
}


public class EventUsingType : EventBaseType
{

}

In the following scenario, EventBaseType typeA will come in as null, whereas EventUsingType typeB will not be null.