No field code
This field can also be used to add new watchers to linked issues, sub-tasks or issues returned by JQL easily.
Alternatively you can use the Watchers field with the additional
The main use case for this virtual field is to add a watcher through the Update or copy field values post function or the Update field action without replacing or removing an existing one.
To learn more about this writable field, check out the adds an assignee as a watcher to every blocking issue use case.