Unable to assign TestRun Assignee same as Issue Assignee

Description: Unable to bulk assign ** TestRun Assignee same as Issue Assignee when issues are assigned to multiple users. Able to assign when Issue Assignee is the single user.

How to reproduce

1. Open a Test Execution
2. Add multiple Tests which are assigned to different users
3. Select all the Tests and try assigning the Tests as 'Issue Assignee'

Actual result/Attachments

Unable to assign the 'TestRun Assignee' for the selected Tests same as the Issue Assignee when issues are assigned to multiple users.  

Expected result

Able to assign the 'TestRun Assignee' the same as the Issue Assignee when the Tests assignee is multiple users.