How to fake Collection.Count with typemock

We use WCSF with CSLA.NET and Typemock 4.3

We have a Class which contains collection object. Based on Collection count some button activation / deactivation happens on presenter and in turn on view.

public ClassA
{
int id
List<string> Names
}

When we test presenter, we mock ClassA. Since ClassA is mocked so does all child objects on ClassA.

In recordering block we say

recorder.ExpectAndReturn(mockClassA.Names.Count, 0)

When we do this we get following:
System.NullReferenceException: Object reference not set to an instance of an object..

get_Count()

We thought what we are doing in recording block is correct, but it doesn't seem like. We don't know how to fix and run the test.

Help is appreciated.