Parent Link JQL does not work with EMPTY keyword

Summary

Searching for the "Parent Link" field using either "IS EMPTY" or "IS NOT EMPTY" returns an incorrect result.

Steps to Reproduce

While having Portfolio active, do the following search:

"Parent Link" is EMPTY

Or

"Parent Link" is not EMPTY

Expected Behavior

• For is EMPTY, only issues without a Parent Link should be returned
• For is not EMPTY, only issues with a Parent Link should be returned

Actual Behavior

The results are returned in an unexplainable way, e.g. issues without a Parent Link appear in is not EMPTY and do not appear in is EMPTY.

Note

The results of the 2 JQLs seem to be complements of each other. For example:

• There're 100 issues, only 5 of which have a Parent Link
• If is not EMPTY returns 20 (or any other number instead of 5)
• Then is EMPTY returns the other 80

Workaround

As introduced by this comment on Feb 5, 2020:
Parent Link is not EMPTY considers 3 types of "parent links": Parent Link from Portfolio, Epics and subtasks. To search issues with only the Parent Link custom field present, exclude the other possible links:

"Parent Link" is not EMPTY AND "Epic Link" is EMPTY

And to further exclude subtasks, if needed:

"Parent Link" is not EMPTY AND "Epic Link" is EMPTY AND issuetype in standardIssueTypes()

Root cause

This happens because the "Parent Link" search keyword is an abstraction of parent links, going beyond the actual custom field with that name.
JPOSERVER-2734 has been created to Change the "Parent Link" search keyword so it doesn't conflict with the "Parent Link" custom field.