I am writing a Groovy script in Scriptrunner for Jira. I want to get a user's display name (full name). I have both the username and the jira user key (i.e. JIRAUSER00000). I'm finding a lot of articles for how to get the username from the full name, but I want to do the opposite because I want to display a user's name, and I think it looks nicer to display their full name rather than just their username. For some reason, I'm not finding a lot about that online. What's the easiest solution for this?
In case this information helps, I am getting the user from a multi-user picker custom field.