Problem/Bug Server stops on start-up

Hello, I recently downgraded my server from 1.15 to 1.8 using buildtools. Everything seemed to be going fine until I ran the server. When I would run it would just randomly stop when generating the world. I tried deleting the world that was used in 1.15. Because of that, it starts loading the spawn but it says Encountered an unexpected exception then gets a nullpointer exception and says stopping server.

Heres my log:
https://pastebin.com/qiuRXFfR


Here is my Crash Report:
https://pastebin.com/eYhKdqGr
Thank you!