diff --git a/Products/ZenHub/server/events.py b/Products/ZenHub/server/events.py
index 6c33cc5f91..07df019e08 100644
--- a/Products/ZenHub/server/events.py
+++ b/Products/ZenHub/server/events.py
@@ -73,18 +73,18 @@ class _CompletedData(_StartedData):
     result = attr.ib(default=_UNSPECIFIED)
 
     def __attrs_post_init__(self):
-        if (
-            sum(
-                1
-                for name in ("result", "error", "retry")
-                if getattr(self, name) is _UNSPECIFIED
-            )
-            != 2
-        ):
+        unspecified = tuple(
+            name
+            for name in ("result", "error", "retry")
+            if getattr(self, name) is _UNSPECIFIED 
+        )
+        if len(unspecified) != 2:
             raise TypeError(
                 "At least one of fields 'result', 'retry', and 'error' "
-                "must be specified"
+                "must be given an argument"
             )
+        for name in unspecified:
+            object.__setattr__(self, name, None)
 
 
 @implementer(IServiceCallReceivedEvent)
diff --git a/Products/ZenHub/server/metrics.py b/Products/ZenHub/server/metrics.py
index 6130722ced..761414e3a7 100644
--- a/Products/ZenHub/server/metrics.py
+++ b/Products/ZenHub/server/metrics.py
@@ -97,7 +97,8 @@ def decrementLegacyMetricCounters(event):
     global _legacy_worklist_counters
     for key in (event.priority, "total"):
         _legacy_worklist_counters[key] -= 1
-        # If the count falls below zero, there's a bug and should be logged.
+        # If the count falls below zero,
+        # there's a bug and should be logged.
         if _legacy_worklist_counters[key] < 0:
             log.warn(
                 "Counter is negative worklist=%s value=%s",