JSONParser.parse() returns None if only 'next_cursor' available.
It looks like someone has broken an if/else when refactoring, which causes python to drop off the end of the function without returning anything useful.

https://github.com/tweepy/tweepy/blame/master/tweepy/parsers.py#L57

diff --git a/tweepy/parsers.py b/tweepy/parsers.py
index 6381912..046cf50 100644
--- a/tweepy/parsers.py
+++ b/tweepy/parsers.py
@@ -54,11 +54,11 @@ class JSONParser(Parser):
             raise TweepError('Failed to parse JSON payload: %s' % e)
 
         needs_cursors = 'cursor' in method.session.params
-        if needs_cursors and isinstance(json, dict):
-            if 'previous_cursor' in json:
-                if 'next_cursor' in json:
-                    cursors = json['previous_cursor'], json['next_cursor']
-                    return json, cursors
+        if needs_cursors and isinstance(json, dict) \\
+                and 'previous_cursor' in json \\
+                and 'next_cursor' in json:
+            cursors = json['previous_cursor'], json['next_cursor']
+            return json, cursors
         else:
             return json
 
['tweepy/parsers.py']