The situation:
def str = \"\"\"
sudo
make me a sandwich!<
I know this was answered a while ago, but here's an alternative for anyone else facing the same issue. The XmlSlurper class has three constructors, a couple of which allow you to specify you want it to be namespace-aware.
public XmlSlurper(boolean validating, boolean namespaceAware)
Declare the slurper by calling new XmlSlurper(false, true).
I hope this is useful to others.