Issue collector template preview is blank when using a custom template

Issue description

When using a custom template, the Issue collector template preview is blank in the issue collector view page, although it is not blank in the edit page.

Steps to reproduce

1. In any project, go to Project Settings -> Issue Collector
2. Click on add an issue collector.
3. From the "Edit issue collector" page, select "Custom" for the Template (note that it is not needed to tick any Custom Fields to reproduce this bug)
4. Notice that the template preview is working on this page.
5. Click on "Update" to save the issue collector
6. Go back to the Project Settings -> Issue Collector page
7. Click on the name of the Issue Collector under the column "Name"

Expected Result

The template preview should not be blank, like it's the case on the "Edit issue collector" page

Actual Result

The template preview is blank from this page:

Note that the template preview is not blank on the "Edit Issue collector" page:

Workaround

No workaround is available; however it is possible to upgrade Jira to 7.12.0 or above (or Service Desk 3.15.0 or above).