When using JQL with "Parent Link" is EMPTY is throwing an error in JQL

Problem

While using JQL to search all the child issues using the "Parent Link" keywords might result in an error "An unknown error occurred while trying to perform a search".

Environment

Steps to Reproduce

1. Navigate to the issue navigator page in Jira Cloud
2. Use any of the custom JQL search with the "Parent Link" keyword -
   e.g

    project in <> and type in <> and "Parent Link" is EMPTY  

3. Page will retun an error
   

   Expected Results

   JQL should return the result as expected

Actual Results

An error is thrown- "An unknown error occurred while trying to perform a search"

Workaround

• Sometimes the search operation works on re-try.

Notes