Here's the crash report from Modrinth, and latest.txt:
crashrep
latest
Note that it mentions BetterNether, too, but the crash only started happening after I updated your mod just now.

I just downgraded to the previous version (2.0.2) and the crash is fixed. Here's the live log of that:
Live Log

And if it's of interest, here's my current list of mods:
list

The crash report is inaccessible and the client log shows no fatal errors.

The crash is unfortunately not fixed.
I have no idea why the link's broken, but here's a new one.

Edit: nvm, Modrinth didn't actually update properly when I hit the update button, it went to 2.0.3, instead of *.4
2.0.4 seems to be fine.

Please update to 2.0.4 and try again.