The server-side soy template 'bitbucket.internal.widget.avatar' provides a very simple but useful component. It:

• Accepts a Person, being either an ApplicationUser or a SimplePerson
• For an ApplicationUser, will find their avatar within Bitbucket Server
• For a SimplePerson, will attempt to find a Gravatar URL for the email address
• Generates the ADG-compliant AUI elements

This may not sound too hard, however Bitbucket developer Felix Haehnel has shown that it takes quite a bit of legwork within a plugin to pull all this together.
https://bitbucket.org/fhaehnel/avatar-list-plugin-sample/src/03d6a1c5e3d6?at=master

All that work, just to render the same avatars that Bitbucket renders for users. Compared to that, using the soy template is a breeze.

Please make it public!