c# - LINQ InsertOnSubmit: NullReferenceException

Question

I have this code:

using DC = MV6DataContext;
using MV6; // Business Logic Layer
// ...

public DC.MV6DataContext dc = new DC.MV6DataContext(ConnectionString);
IP ip = new IP(Request.UserHostAddress);
dc.IPs.InsertOnSubmit(ip);
dc.SubmitChanges();

// in Business Logic layer:
public class IP : DC.IP {
  public IP(string address) { ... }
}

Upon attempting to InsertOnSubmit(ip), I get a NullReferenceException (Object reference not set to an instance of an object). dc is not null; ip and all properties of ip are not null; though some are empty.

VS2008 won't let me step into InsertOnSubmit, so I have no way of knowing what specifically is null when being evaluated. What gives?

Note: I have checked, and all Linq.EntitySets created by FK relationships are present and non-null.

Answer 1

Actually it's better to add a call to your constructor that also calls the generic constructor such as:

public IP(string address) : this() {
...
}