JQL issueLinkType is inconsistent when using != or NOT IN operators

Summary

When filtering issues by issueLinkType the results are inconsistent when using the != and NOT IN operators.

Steps to reproduce

1. Do an advanced search and compare the results when filtering all issues in a project and all issues in the same project excluding issues with a specific issueLinkType;
2. Issues in the project can be checked:

project in ("Project A")

3. Issues in a specific issueLinkType:

project IN ("Project A") AND issueLinkType = "relates to"

4. Now run with the != or NOT IN clause:

project IN ("Project A") AND issueLinkType != "relates to"

5. Try by including an IS EMPTY clause:

project IN ("Project A") AND (issueLinkType != "relates to" OR issueLinkType is EMPTY)

Expected results

The != or NOT IN operators should return the difference between the first and second queries.

Actual Results

The values are inconsistent.

Workaround

• For similar behavior to what would be expected results of an "IS EMPTY" or "IS NOT EMPTY" you can use the workaround noted in JRACLOUD-72795 and do a filter "!=" referance to a saved filter to exclude any issue with the set list of link types, like the following:
• Create a saved filter including a list of all the current link types EXE:

  saved filter = issueLinkType in ("all", "of", "the Issue Link Type Names", "as a comma separated", "List", "using Both the" "Outward Description" "And" "Inward Description")
  

• Then in your final JQL:

  Project = "Project A" AND filter != <filter_ID>