paper previously migrated away from using executeIfPossible as this throws a
RejectedExecutionException when the server is shutting down, which is then picked
up by the Connection handler object and causes the player to be kicked without
the intended disconnection message that comes from commands such as /stop, /restart
This was fine, because previously changes made in spigot would just prevent these
packets from being executed anyways. Instead, we'll just use a marker exception
to try to detect this specific state.
Shane Freeder