Better display of the Parent Issue field in jiraissue macro in Confluence

Steps to Reproduce

1. Create a Confluence page
2. Add the JIRA issue macro and query for issues in a JIRA project that uses JPO
3. Select the field Parent Issue to display

Expected
The parent issue key should be shown. Maybe even as a link to the issue

Actual
A Java object ref is shown

Request: please update the JPO object to allow Confluence to render it properly