diff --git a/StatsCrosslet-DS/StatsCrosslet.py b/StatsCrosslet-DS/StatsCrosslet.py
index 54c8de4891b57fa7e8d728e8099a6704bfd26080..da7d9407d8924cb5fdd68e738326d971701bbc4d 100644
--- a/StatsCrosslet-DS/StatsCrosslet.py
+++ b/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.")