CarryOnFix

The crash: Your Minecraft 1.21.1 NeoForge server was crashing every time a player used Carry On to pick up an entity or block. The root cause was a NullPointerException inside StringTagVisitor.visitCompound(): Minecraft tried to sort the NBT keys of whatever was being carried, but one of those keys was null, causing Java's TimSort to explode.

The fix: We built a small standalone NeoForge mod called CarryOnFix that uses a Mixin to intercept the Collections.sort() call, strip any null entries from the list, and then let the sort proceed normally. Two lines of actual logic.

Mod features:

• Server-side only — clients don't need it installed, just drop the jar in the server's mods/ folder
• No extra dependencies
• Compatible with NeoForge 21.1.228 / Minecraft 1.21.1

Bumps along the way:

• IExtensionPoint and NetworkRegistry no longer exist in NeoForge 21.1 and caused a compile error — we removed them entirely, since displayTest = "IGNORE_ALL_VERSION" in neoforge.mods.toml is all you need to declare a server-side-only mod in modern NeoForge.