Python is not C++, it does not know Null but only None

StatsCrosslet-DS/StatsCrosslet.py

@@ -208,7 +208,7 @@ class StatsCrosslet(Device):
         self.debug_stream("Waiting for data acquisition thread to shut down...")
         self.data_read_loop.join()
         self.debug_stream("Waiting for data acquisition thread to shut down, done")
-        if self.client is not Null:
+        if self.client is not None:
             self.client.close_session()
             self.client_secure_channel()
         self.debug_stream("Shutdown done.")