Mod Version-Minecraft Version
Minecraft 1.19.2, Better Furnaces Reforged v0.2.1
Mod Loader Version
Fabric 0.14.21

Bug/Glitch Occurrence Context
Server crashes when Auto-Input/Output/Factory upgraded furnaces are adjacent to various blocks such as Create fluid tanks or the Alternator from Create Crafts & Additions.

*Crash Report
crash-2023-06-20_21.22.29-server.txt

What happened wrong
I believe the issue is related to the fact that you're calling other.iterator() on line 40 of fabric/BetterFurnacesPlatformImpl.java, immediately before checking for other being null; Moving this after the check should fix these crashes.

This is exactly the bug you pointed out, it has been fixed in the later minecraft versions of the mod.
It will be fixed in 1.19.2-0.2.2, in the update that will bring the features of 1.19.4-0.1.4 :)