IssueNotifier should us an array when setting the fixVersions property of an issue. There is currently code in JiraProject.encodeProperty that enables code to use a plain string fox fixVersions, but such code will then break when using a TestIssueTrackerIssue (that does not feature any special encoding of the fixVersion). To allow the code to work with both tests and production JIRA instances the production should use an array and not a string when setting fixVersions.