Fix the error case Qingxin pointed out.

spec.bs

@@ -4306,8 +4306,9 @@ runs; this method exists as an abstraction to help add that.
 
 <div algorithm>
 To <dfn>commit private aggregation contributions</dfn> given an [=Private Aggregation
-contributions=] |onEventMap|, a [=reporting bid key=] |bidKey|, and a [=reporting context=]
+contributions=] or null |onEventMap|, a [=reporting bid key=] |bidKey|, and a [=reporting context=]
 |reportingContext|:
+  1. If |onEventMap| is null, return.
   1. [=map/For each=] |event| → |contributions| of |onEventMap|:
     1. Let |key| be (|bidKey|, |event|).
     1. If |reportingContext|'s [=reporting context/private aggregation on event contributions=][|key|]
@@ -5696,7 +5697,8 @@ of the following global objects:
       and |privateAggregationCoordinator|.
     1. Let |argumentsJS| be the result of [=converting a Web IDL arguments list to an ECMAScript
       arguments list|converting=] |arguments| to an ECMAScript arguments list. If this
-      [=exception/throws=] an exception, return « "null", null, null, null ».
+      [=exception/throws=] an exception, return « "null", null, null, null, null,
+      |executionMetrics| ».
     1. Let |executionMetrics| be a new [=execution metrics=].
     1. Let (|result|, |executionMetrics|'s [=execution metrics/script timed out=]) be the
       result of [=evaluating a script=] with |realm|, |script|, |functionName|, |argumentsJS|,