From 8351869346707acf53b473701988782b2dc8bea3 Mon Sep 17 00:00:00 2001
From: David Baumgold <david@davidbaumgold.com>
Date: Tue, 22 Apr 2014 13:30:49 -0400
Subject: [PATCH] Fixes #3409

---
 common/djangoapps/monitoring/signals.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/common/djangoapps/monitoring/signals.py b/common/djangoapps/monitoring/signals.py
index 6068a2347a..f870ff1c54 100644
--- a/common/djangoapps/monitoring/signals.py
+++ b/common/djangoapps/monitoring/signals.py
@@ -125,8 +125,10 @@ def m2m_changed_metrics(sender, **kwargs):
     if 'model' in kwargs:
         tags.append('target_class:{}'.format(kwargs['model'].__name__))
 
+    pk_set = kwargs.get('pk_set', []) or []
+
     dog_stats_api.increment(
         'edxapp.db.model',
-        value=len(kwargs.get('pk_set', [])),
+        value=len(pk_set),
         tags=tags
     )