Avoid failures if no children found

node-daemon/pvcnoded/objects/MonitoringInstance.py

@@ -317,9 +317,11 @@ class MonitoringInstance(object):
             return
 
         # Clean up any old plugin data for which a plugin file no longer exists
-        for plugin_key in self.zkhandler.children(
+        plugins_data = self.zkhandler.children(
             ("node.monitoring.data", self.this_node.name)
-        ):
+        )
+        if plugins_data is not None:
+            for plugin_key in plugins_data:
                 if plugin_key not in self.all_plugin_names:
                     self.zkhandler.delete(
                         (