When Passing An Object As An Argument To A Method, String Properties Are Populated But Integers Are Null

I have a class and method exposed to a client asp.net app. The class looks like

<DataContract()> _
Public Class Class1
Private v_string As String
Private v_integer As Integer

[code]....

The method is declared as

<OperationContract()> _
Function GetStuff(ByVal bar As Class1) As String

In the client code I create an instance of Class1 and set the values for v_string and v_integer, but using Wireshark to look at the xml being sent to the server only a value for v_string is being sent as part of Class1. I'm guessing this is because it considers the value of v_integer to be null/not set. Here is an example of the client code.

Dim MyService as New Service1.ServiceClient
Dim test as New Service1.Class1
test.P_integer = 1

[code]....

how different types are passed/used since Integer is a intergral type and String is a class, but can't seem to work out what to do to fix the problem.