Auto-assigning issues in JIRA Cloud transition throwing errors

Summary

If a workflow is set up with a post function that automatically maps the assignee to a role or another field using JIRA Misc Workflow Extensions an error is currently being thrown when transitioning the issue.

Steps to replicate

1. Set up a workflow with a post-function that sets the assignee to the contents of another field, such as reporter.
2. Transition an issue so that post-function occurs

Expected Result

Assignee changes

Actual Result

Error is thrown in the transition 'unable to copy value from reporter to assignee'

When editing the post-function the following value is shown:

$textutils.htmlEncode(${fieldValue})

Workaround

A workaround for now is to remove the post-function that automatically assigns issues and manually assign issues instead. If you do not want to trust all users to assign issues then your best bet is to restrict assign issue permission.

If the 'create issue originally' post function exists (in case it's the 'create' transition), moving the auto-assigning post function up, before the 'create' one has worked in some cases as a workaround.