Oh right, this is the <code>dummy_virsh.dumpxml</code> so it's different.  I put that there because I didn't want to use the <code>mock</code> module, however, the <code>dummy_virsh.dumpxml</code> should mirror the real one.  If it would raise an exception when given a <code>''</code> name, then <code>dummy_virsh.dumpxml</code> should also.