get_pickleable_etype must actually return a value... Closes #1556

celery/utils/serialization.py

@@ -151,6 +151,8 @@ def get_pickleable_etype(cls, loads=pickle.loads, dumps=pickle.dumps):
         loads(dumps(cls))
     except:
         return Exception
+    else:
+        return cls
 
 
 def get_pickled_exception(exc):