The "hasHandler" information for exceptions is lost when notifying the WebScriptDebuggerDelegate.
It may be useful for the delegate to know if the exception was uncaught or not.
The information is available, before calling the delegate, but it is ignored (note "hasHandler"):
Inspector uses that information to identify an "uncaught" exception:
Looks like this is being handled in:
<http://webkit.org/b/52104> Would like script debugging protocol method to differentiate between caught and uncaught exceptions
*** This bug has been marked as a duplicate of bug 52104 ***