RFR: 1616: Improve error message when an author isn't found in GitLab

[Zhao Song]

On Wed, 5 Oct 2022 16:39:42 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

>> Improved the error message in GitLabMergeRequest:author
>
> forge/src/main/java/org/openjdk/skara/forge/gitlab/GitLabMergeRequest.java line 85:
> 
>> 83:             return author.get();
>> 84:         } else {
>> 85:             throw new IllegalArgumentException("Unknown username: " + username);
> 
> I don't think IllegalArgumentException is correct here. It's meant to be thrown when a method receives a bad argument, but this method doesn't take arguments. We don't really have a reason to define a new exception type either, so a plain `RuntimeException` is probably better, at least for now.
> 
> I'm usually for short and concise messages, but in this case I think we can add some more details. Something like `"Author of merge request unknown: " + username`

Ok, I also thought about the type of exception yesterday. I was thinking that the username is an argument of `user(username)`, but throw exception in method `user` is a little complex. 

I will change it to RuntimeException and make the error message have more details.

-------------

PR: https://git.openjdk.org/skara/pull/1390