Batched Notifications do not work with the Toolkit add-on field type "Participants of an issue"

Issue Description

If Batched Notifications are enabled, no notification will be sent to the users added to the field of type Participants of an issue which comes from the Atlassian Lab add-on Toolkit plugin for Jira.

Notes

• This field should not be confused with the Request Participants field that comes with Jira Service Management projects.
• This bug impacts any type of notification event (issue commented, issue updated, etc...)
• If batched notifications are disabled, notifications will be sent to the users added to the field of type Participants of an issue

Environment

• Replicable on Jira Server/Data Center
• Only when notification batching is enabled
• Replicable on any Jira version from 8.13.0
• Not replicable on Jira 8.0.x

Steps to replicate

1. Install Jira on 8.0.0 or any higher version
2. Create 2 users, for example:
   • admin
   • julien
3. Enable batched notifications in ⚙ > System > Batching email notifications
4. Create a new project
5. Install the add-on Toolkit plugin for Jira via the page ⚙ > Manage apps > Find new apps
   
6. Go to ⚙ > Issues > Custom Fields, create a new field of type Participants of an issue, and add it to all the screens of the project created earlier. Let's call this field Participants
   
7. Edit the Notification Scheme associated to the project and add the custom field Participants to the Issue Commented event
   
8. Create a new ticket as follows:
   • Make sure that the user julien is included in the Participants field, but not in the Assignee field nor in the Reporter field
     • Since it is a calculated field, this field can't be manually edited from the UI
     • You need to log in as julien, have this user add a comment to the ticket, and this user will be automatically added to the field
9. Add a new comment to this ticket as the user admin
   
10. Wait for about 15min

Expected result

The user julien should receive a new notification about the new comment.

Actual result

• No notification is sent to this user
• When enabling Outgoing Mail DEBUG, we see in the Jira Outgoing Mail Log file, that the Batched Notification functionality is unable to find the "recipients" of the notification (the recipient parameter shows as empty: Recipients: [])

  2023-06-05 12:05:59,906+0000 DEBUG [] JIRA-INFORM-Thread-3 anonymous 568x855x1 1ynk85n 172.29.215.197,172.50.0.2 /rest/api/2/issue/SCRUM-25/comment [c.a.m.o.c.a.j.p.i.batching.recipients.JiraNotificationSchemeRecipientProvider] Getting recipients for com.atlassian.jira.event.issue.IssueEvent@3f401591[issue=SCRUM-27,comment=<null>,worklog=<null>,changelog=[GenericEntity:ChangeGroup][issue,10200][author,admin][created,2023-06-05 12:05:59.74][id,10301],eventTypeId=2,sendMail=true,params={eventsource=action, baseurl=https://linux-43770.prod.atl-cd.net/jira},subtasksUpdated=true,spanningOperation=Optional.empty]
  2023-06-05 12:05:59,908+0000 DEBUG [] JIRA-INFORM-Thread-3 anonymous 568x855x1 1ynk85n 172.29.215.197,172.50.0.2 /rest/api/2/issue/SCRUM-25/comment [c.a.m.o.c.a.j.p.i.batching.recipients.JiraNotificationSchemeRecipientProvider] Recipients: []
  2023-06-05 12:05:59,910+0000 DEBUG [] JIRA-INFORM-Thread-3 anonymous 568x855x1 1ynk85n 172.29.215.197,172.50.0.2 /rest/api/2/issue/SCRUM-25/comment [c.a.m.o.c.a.j.p.inform.performance.MeasurementWorkerFactory] PerformanceEvent{type=CONVERTING_TO_DB, duration=4 ms, success=true, parameters={parameters.size=17}}
  2023-06-05 12:05:59,916+0000 DEBUG [] JIRA-INFORM-Thread-3 anonymous 568x855x1 1ynk85n 172.29.215.197,172.50.0.2 /rest/api/2/issue/SCRUM-25/comment [c.a.m.o.c.a.j.p.inform.performance.MeasurementWorkerFactory] PerformanceEvent{type=SAVING_TO_DB, duration=5 ms, success=true, parameters={parameters.size=17}}
  2023-06-05 12:05:59,916+0000 DEBUG [] JIRA-INFORM-Thread-3 anonymous 568x855x1 1ynk85n 172.29.215.197,172.50.0.2 /rest/api/2/issue/SCRUM-25/comment [c.a.m.o.c.a.j.p.inform.performance.MeasurementWorkerFactory] PerformanceEvent{type=JIRA_EVENT_PROCESSING, duration=10 ms, success=true, parameters={savedEventsCount=1}}
  

Workaround

Workaround 1

If using the field Participants of an issue is crucial to your operation, then the only workaround is to disable notification batching in the whole Jira instance.

Workaround 2

If using the field Participants of an issue is not crucial, use instead a field of type user picker in the notification scheme