EssXDiscord Advancement Notifications do not work on 1.12.2

[triagonal]

Type of bug

Error in console

/ess dump all output

https://essentialsx.net/dump.html?id=5818a368c2cc46a9aca556188341bffc

Error log (if applicable)

https://paste.gg/p/anonymous/0c747d0be3af4abf93d8cd1ade502140

Bug description

essxdiscord advancement notifications fail to enable correctly on 1.12.2

Steps to reproduce

1. Set up discord bot (token, guild, channels)
2. Attempt to run discord bot
3. Observe error

Expected behaviour

jroy writes working code

Actual behaviour

https://cdn.discordapp.com/attachments/876902758366736457/906750352790003742/jroy_development.mp4