diff --git a/circle/firewall/models.py b/circle/firewall/models.py
index 7a3d857..55ce901 100644
--- a/circle/firewall/models.py
+++ b/circle/firewall/models.py
@@ -971,7 +971,7 @@ class Firewall(models.Model):
                              "maybe syslog isn't readble by firewall worker")
         except:
             logger.exception("get_dhcp_clients failed")
-        return None
+        return {}
 
 
 class Domain(models.Model):