You can set IsRequired = True and EmitDefaultValue = False.
This will tell Wcf runtime to serialize data member but do not serialize default values, i.e. do not serialize null values for reference types, 0 for integers, etc.In effect, a runtime exception will be thrown if the data member has not been assign a value during serialization. If we do not set EmitDefaultValue toFalse CLR will set it to zero (default for integer) automatically.
Referance :-
http://social.msdn.microsoft.com/Forums/en-US/wcf/thread/d9e45449-cc50-42e2-b955-75ab86f01d4f
http://social.msdn.microsoft.com/Forums/en-US/wcf/thread/d9e45449-cc50-42e2-b955-75ab86f01d4f
