fix index error on no topics

CHANGELOG.md

@@ -2,6 +2,7 @@
 - Changed content type to better reflect that this is a custom stream
 - Switched to internal counter for number of requests served
 - Added max payload size setting
+- Fixed an issue where payloads with no topics would cause an indexing error
 
 # 0.4.5
 - Better handling of errored subscriber connections

pypubsub.py

@@ -236,7 +236,7 @@ class Payload:
         self.private = False
 
         # Private payload?
-        if self.topics[0] == 'private':
+        if self.topics and self.topics[0] == 'private':
             self.private = True
             del self.topics[0]  # Remove the private bit from topics now.