testing-harness MavenProjectStub

[Brian E. Fox]

I'm using the project stub in the testing-harness project. I'm curious
about the decision to default all collections to return strings:
 
    public Set getArtifacts()
    {
        return Collections.singleton( "" );
    }
 
Wouldn't it make more sense to return an empty set than a set with a
string? I can't see how this would ever work since isn't every use of
the resulting set going to cast the object to an Artifact?
 
Anyone able to shed light on this?