How about adding this?

```csharp
[Fact]
public void CanNotAmendACommitInAWayThatWouldLeadTheNewCommitToBecomeEmpty()
{
    string repoPath = InitNewRepository();

    using (var repo = new Repository(repoPath))
    {
        Touch(repo.Info.WorkingDirectory, "test.txt", "test\n");
        repo.Index.Stage("test.txt");

        repo.Commit("Initial commit", Constants.Signature, Constants.Signature);

        Touch(repo.Info.WorkingDirectory, "new.txt", "content\n");
        repo.Index.Stage("new.txt");

        repo.Commit("One commit", Constants.Signature, Constants.Signature);

        repo.Index.Remove("new.txt");

        Assert.Throws<EmptyCommitException>(() => repo.Commit("Oops", Constants.Signature, Constants.Signature,
            new CommitOptions{ AmendPreviousCommit = true }));
    }
}
```