diff --git a/flowmon-ads/warden3_flowmon_ads_filer.py b/flowmon-ads/warden3_flowmon_ads_filer.py
index 94adf3e99ad0d22f198661b79bf4cf3657bfa33a..f62913ac61e8d940ee11c7d0e89060b0104bd14d 100755
--- a/flowmon-ads/warden3_flowmon_ads_filer.py
+++ b/flowmon-ads/warden3_flowmon_ads_filer.py
@@ -63,7 +63,10 @@ def int_list(il):
     return [int(i.strip()) for i in il.split(",")]
 
 def str_list(sl):
-    return [s.strip() for s in sl.split(",")]
+    if sl:
+        return [s.strip() for s in sl.split(",")]
+    else:
+        return []
 
 def sum_int(s):
     return int(sum(float(val) for val in s))