fix mangling for addresses that are None
diff --git a/qpid/messaging/endpoints.py b/qpid/messaging/endpoints.py
index 8bddc96..62423ca 100644
--- a/qpid/messaging/endpoints.py
+++ b/qpid/messaging/endpoints.py
@@ -710,7 +710,7 @@
       self.connection._remove_session(self)
 
 def _mangle(addr):
-  if addr.startswith("#"):
+  if addr and addr.startswith("#"):
     return str(uuid4()) + addr
   else:
     return addr