Using the %fn modifier causes this error. When I instead use%n everything works perfectly. I have yet to try %dn but I have a feeling it will work.

Probably relevant: I don't have any prefixes/suffixes set in players.yml.

Let me know if you need more information such as configuration files.

Yeah, I'm aware. I haven't yet added the %fn processor for the plugin yet. I'm lazy.

I can relate to your laziness. I figured you may but I always like to file a bug report just to be safe. 😄

Quick question while I'm here, does %dn fall back to %n if a player doesn't have a display name? If not, feature request.

Yeah. %dn will show their name if it's empty or the same. In the event that their name is set to null, though.. I don't know.