Smart value {{parent.watchers}} is not working for Next-gen projects

Issue Summary

The Smart value parent.watchers is not working in the automation rules of Next-gen projects.

Steps to Reproduce

1. Navigate to a Next-gen project > Project settings > Automation
2. Click to create a new automation rule like the one below:
   
3. Create a parent issue in the next-gen project and add some watchers
4. Finally, create a sub-task issue under that parent

Expected Results

The watchers are properly copied to the sub-task.

Actual Results

The watchers are not copied to the sub-task and the rule returns the following error:

Workaround

None so far.