At work, my username is my userId so it's my git user.name and my JIRA/Stash username, but my displayName is "FirstName LastName".
When creating a repository in Stash, it proposes to set my git user.name to my displayName.
If I use my userId, the commits listing page still use the right avatar from Gravatar but display my userId. Could be better to display my displayName (maybe with a link to the corresponding profile).

So Stash should match my user on my userId and/or displayName and always display the displayName.