bug fix

rowers/dataprep.py

@@ -484,7 +484,7 @@ def join_workouts(r,ids,title='Joined Workout',
         w = Workout.objects.get(id=id)
         w.duplicate  = False
         w.save()
-        if "duplicate" in message:
+        if message is not None and "duplicate" in message:
             message = ""
 
     return (id, message)