Hey Luck, testing Java 11 and it seems this plugin is the only one shooting an error for me.
Can't even see it in the logs, seems to be a client side thing on the local machine:
https://i.imgur.com/Rf461Qz.png

This is me loading up the server on my test box, all other plugins work fine (over 40), just luck perms being weird for some reason.

Previously was using Java 8

Pretty much an exact duplicate of #1290.

Edit: see this response from Luck on #952:

You can ignore the warning for now.

There's not currently any alternative methods or APIs available to achieve the same thing without reflection (to my knowledge)

All illegal access operations will be denied in a future release

Not sure when/if that will happen - I'm hoping that there with be an alternative method available by then. Until it happens, there's not really much I can do.