Blockwave mechanic stopped working and started giving an error

Summary

The blockwave mechanics stopped working (it worked in previous versions of the plugin or minecraft) and started giving an error.

Steps to reproduce

1. Add this skill (https://pastebin.com/BZPvP3Cx) in your NameOfFileSkills yml
2. Link it with mob or player (For player use MMOCore)
3. Activate skill
4. Get this error (https://pastebin.com/3BAY9Ptz)

Server log file

https://pastebin.com/Dh01t9XE