As a Stash User, I want a more explicit error message when cascading merge fail in order to be able to understand that error is related to cascading option and I can create properly named releases branches or remove cascading option from my project

When a Stash user use the cascading option on branches that are not following the semantic versioning rules, he recieves a very unexplicit error message when merging: "An error occurred"

the internal error is:
2014-10-16 15:19:46,947 ERROR [AtlassianEvent::thread-5] tserot
@VKVT7Cx919x173559x11 2z42m0 172.16.248.123,172.16.141.210 "POST
/rest/api/latest/proj
ects/CAR/repos/gch/pull-requests/11/merge HTTP/1.0"
c.a.s.i.e.AsyncBatchingInvokersTransformer There was an exception thrown
trying to dispatch event
'com.atlassian.stash.event.pull.PullRequestMergedEvent[source=com.atlass
ian.stash.internal.pull.PullRequestServiceImpl@1639b135]' for the
invoker 'Sin
gleParameterMethodListenerInvoker

{method=public void com.atlassian.stash.internal.branch.automerge.AutoMergePullRequestProces sor.onPullRequestMerged(c om.atlassian.stash.event.pull.PullRequestMergedEvent), listener=com.atlassian.stash.internal.branch.automerge.AutoMergePullRequ estProcessor@5aebfb30}

'
.
java.lang.RuntimeException: index (-1) must not be negative
at
com.atlassian.event.internal.SingleParameterMethodListenerInvoker.invoke
(SingleParameterMethodListenerInvoker.java:54) ~[atlassian-event-2.
3.5.jar:na]

the index is -1 because the rules for cascading feature are not
respected and so Stash is not able to build the list of branches where
it can cascade the changes.

A more explicit message may be usefull to help Stash user knowing that it is, at least, an error related to cascading.

In my case, the merge was successfull, but cascading sent this error message. As the cascading setting was only a try not removed on the repository, it may have been usefull to directly give the real source of the problem to help user reacting accordingly.