Shopkeepers 2.4.1
Paper Spigot - 1.13.2 - 521

https://pastebin.com/Yx7x1cSn

I just tried and cannot reproduce the issue on a freshly setup server..

Make sure that there are no other errors before the above error inside your server log. In casethe issue is something else, and this is only a side effect.

Also: Can you try it without other plugins, besides Shopkeepers and Citizens? And if you can still reproduce it there, try it on fresh server (with default config/setup).

The steps I take to reproduce are, while the server was on I changed "enable-citizen-shops: false" to "enable-citizen-shops: true" in the config, then saved it then did "/shopkeepers reload", then I did /shopkeepers admin npc then the WARN came up. So maybe the reload caused it?

Im using Paper Spigot 1.13.2 - Build 521
https://papermc.io/ci/job/Paper-1.13/

I did the exact same steps (reload, same paper version). So the issue has to be something else, specific to your server/setup (other plugins, server configs, plugin configs, previous errors, ..)

oh also it was all happening inside a WorldGuard region, that was the other condition

ok ill further investigate

Here was someone with the same error: CitizensDev/Citizens2#1626
And here as well: CitizensDev/Citizens2#1039
Like said in that ticket: Can you try without other plugins?

Yeah I'll further investigate and I'll try without other plugins

Seems to be Citizens related. Can you create a citizens npc (with the citizens command), or is this failing as well?

I can still create citizens as normal,
using this build of citizens [00:46:49 INFO]: Version: 2.0.24-SNAPSHOT (build 1616)

http://ci.citizensnpcs.co/job/Citizens2/

Closing this, as this doesn't seem to be an issue with Shopkeepers.