Index: root/xen-unstable.hg/tools/python/xen/util/security.py
===================================================================
--- root.orig/xen-unstable.hg/tools/python/xen/util/security.py
+++ root/xen-unstable.hg/tools/python/xen/util/security.py
@@ -608,6 +608,11 @@ def list_labels(policy_name, condition):
             label = line.split()[3]
             if label not in labels:
                 labels.append(label)
+
+    f.close()
+    if '__NULL_LABEL__' in labels:
+        labels.remove('__NULL_LABEL__')
+
     return labels