So I have both classes in the same diagram.  I can add persistent associations just fine.  The extension method works as desired.  The problem I'm having is with derived associations.  I cannot get them to work.  My latest attempt gives an error in the extender code:

private static void EnsureMemberIndex(Vco.PartyPackage.Application obj) {
    if ((memberIndex == -1)) {
        memberIndex = OtherEndExtenderHelper.GetMemberIndexOfOtherEnd(obj, typeof(Vco.ProductPackage.Product), Vco.ProductPackage.Product.Eco_LoopbackIndices.Application2);
    }
}

I get an "Object reference not set to an instance of an object" error when OtherEndExtenderHelper.GetMemberIndexOfOtherEnd is called.

Has anyone got a derived association between two packages to work?

Thanks,

Brian

The bug report details things and has the sample app attached.

I just want to add that I love the concept of using extension methods to access associations from classes that know nothing of the class on the other end.  It really provides a nice way to break models up into reusable modules.  I can't wait until Microsoft finally implements extension propterties.  My fingers are crossed for .NET 5.

Brian