zeroconf: compare singleton using is

hgext/zeroconf/Zeroconf.py

@@ -1145,7 +1145,7 b' class ServiceInfo(object):'
                         value = 0
 
                 # Only update non-existent properties
-                if key and result.get(key) == None:
+                if key and result.get(key) is None:
                     result[key] = value
 
             self.properties = result