Customers are unable to share request if "Assign issue" permission is not provided

Summary

If "Assign issue" permission is not provided to Portal Customers, they will be unable to share request with other customers.

Steps to Reproduce

1. Create a Service Desk Project
2. Grant User's Permission to share request to anyone.
3. Go to the permission scheme and remove the "Assign Issue Permission" from "Service desk customer - portal access" role
4. Logged as a Portal Customer, create a request and try to share it.

Expected Results

Once you enter the email address of the person you want to share the request with, you hit "Add" and the participant should be included on the ticket.

Actual Results

Hitting "Add" will not include the other user as a participant.

Workaround

JIRA Service Desk will detect this permission inconsistency and will show a pop-up window, suggesting the resolution of the issue.