Editing an issue with cascading select without child option clears the parent option

Issue Summary

Submitting the edit form for an issue containing a cascading select without child option in Jira 8.8.1 and 8.9.0 clears the parent option.

Steps to Reproduce

1. Create a cascading custom field with any parent and child options
2. Create an issue or edit any existing issue so that the parent option is set and child option remains "None"
3. Open issue edit form ("Edit" button on the issue view) and submit it without any changes

Expected Results

The issue is not changed

Actual Results

The parent option was removed from the issue

The information about the removed parent option is stored in the issue history

Workaround

You can edit a velocity template for the cascading select custom field to fix this issue.
To do so:

1. open the file <JIRA_INSTALLATION>/atlassian-jira/WEB-INF/classes/templates/plugins/fields/edit/edit-cascadingselect.vm.
2. There, edit the code on line 48 from:

   •         #if ($databaseParent && !$hadSelectedChildOption)
     

   • to:

             #if ($databaseChild && !$hadSelectedChildOption)
     

3. After applying the change, save the file and restart the Jira node.

In Jira DC, the workaround needs to be applied separately for every node.