Type of bug

Error in console

/ess version output

[23:27:47 INFO]: Server version: 1.8.8-R0.1-SNAPSHOT git-Spigot-db6de12-18fbb24 (MC: 1.8.8)
[23:27:47 INFO]: EssentialsX version: 2.19.0-dev+106-214d07c
[23:27:47 INFO]: Vault is not installed. Chat and permissions may not work.
[23:27:47 INFO]: You are running a server with limited API functionality. EssentialsX will still work, but certain features may be disabled.
[23:27:47 INFO]: Fetching version information...
[23:27:47 INFO]: You're running the latest EssentialsX dev build!

Server startup log

https://paste.gg/p/anonymous/a3fc079cf0fe42d6bccac6c3bc3ac18c

EssentialsX config files

https://paste.gg/p/anonymous/178d9f61f06f4ff1896c214fef2e1d02

Error log (if applicable)

https://paste.gg/p/anonymous/5879bb9928c14a668a98dc37e368f3d2

Bug description

After running /kit twice with kit-auto-equip enabled, produces an error on 1.13.2 and prior due to Material.isAir() not existing in these versions, and does not give kit

Steps to reproduce

Tested on 1.8.8 Server

1. Create a kit and enable kit-auto-equip
2. /kit - gives you kit
3. running it again doesn't give you kit and errors

Expected behaviour

No errors

Actual behaviour

Produces an error and doesn't give new kit