diff --git a/ContentDirectory.py b/ContentDirectory.py
index 0a9b04f..5962820 100644
--- a/ContentDirectory.py
+++ b/ContentDirectory.py
@@ -101,6 +101,8 @@ class ContentDirectoryControl(UPnPPublisher, dict):
 
 	def addContainer(self, parent, title, klass = Container, *args, **kwargs):
 		ret = self.addObject(parent, klass, title, *args, **kwargs)
+		if ret is None:
+			return
 		self.children[ret] = self[ret]
 		return ret