Reject with no such user context in setExtraHeaders and addDataCollector

Author: juliandescottes

index.bs

@@ -8759,7 +8759,7 @@ The [=remote end steps=] given |session| and |command parameters| are:
 
        1. Let |user context| be [=get user context=] with |user context id|.
 
-       1. If |user context| is null, return [=error=] with [=error code=] [=invalid argument=].
+       1. If |user context| is null, return [=error=] with [=error code=] [=no such user context=].
 
 1. Let |collector| be a [=network/collector=] with
    [=network-collector/max encoded item size=] field set to |max encoded item size|,
@@ -9695,7 +9695,7 @@ The [=remote end steps=] given |session| and |command parameters| are:
 
     1. Let |user context| be [=get user context=] with |user context id|.
 
-    1. If |user context| is null, return [=error=] with [=error code=] [=invalid argument=].
+    1. If |user context| is null, return [=error=] with [=error code=] [=no such user context=].
 
     1. [=list/Append=] |user context| to |user contexts|.