Issue

I wanted to build an enderman farm. The design I picked required the farm to be at the End, and as low as possible. I modified the design a bit to place sophisticated barrels below some hoppers. The barrels were placed at the lowest possible building height. I had created some advanced hopper upgrades to move items from one barrel to the next. As soon as I placed the first advanced hopper upgrade in the first barrel, the server crashed. Restarted the server, logged in again, same problem. As soon as the server starts, it crashes.

Logs

No reason to paste the whole log. The following line is more than enough, since you must have already guessed the problem.
Caused by: java.lang.NullPointerException: Cannot invoke "java.util.List.iterator()" because the return value of "net.p3pp3rf1y.sophisticatedstorage.upgrades.hopper.HopperUpgradeWrapper.getItemHandlers(net.minecraft.world.level.Level, net.minecraft.core.BlockPos, net.minecraft.core.Direction)" is null
Obviously, when the block checks which block is below it, it gets null instead of air or some other block, and it doesn't handle graciously that case.

sophisticatedcore-1.20.1-0.6.18.597
sophisticatedbackpacks-1.20.1-3.20.5.1039
sophisticatedstorage-1.20.1-0.1033.861

I'll get the latest versions for 1.20.1 and try to log in again. I'll let you know of the results.

What versions of mc / storage are you on?

All working properly! I noticed some extra features as well! Nice work!