Use case
Return the display name of the previous assignee.
Expression
Create and configure a Smart field using this expression in Jira expression parsing mode:
issue.changelogs.map(i=>i.items).flatten().filter(i=>i.field=="assignee").length>0 ? issue.changelogs.map(i=>i.items).flatten().filter(i=>i.field=="assignee").map(a=>a.fromString)[0] : ""
