I'm trying to Mock my Repository and I have a function that calls it that looks like this:

```
return _mailingListRepository.Find(ml => ml.EmailAddress == email).Any();

```

I setup my Mock Repository like this:

```
_mailingListRepositoryMock.Setup(m => m.Find(It.IsAny<Expression<Func<MailingList, bool>>>())).Returns((IEnumerable<MailingList>) null);

```

But it then throws an exception: Value cannot be null. What should I return in my setup?