Fastutil NullPointerException: "this.wrapped" is null (Async Map/Item Modification)

What the log looks like

java\.lang\.NullPointerException: Cannot invoke "it\.unimi\.dsi\.fastutil\.objects\.ObjectArrayList\.get\(int\)" because "this\.wrapped" is null

How to fix it

1. Check the stack trace right below the error: if you see 'CraftAsyncTask' or 'generated an exception while executing task', note the plugin or mod name listed in the trace (for example, CMI's armor animation feature) and update or disable that feature.
2. If the stack trace only shows 'PacketEncoder' and 'CompoundTag.copy' without naming a culprit, look for plugins or mods that dynamically update player inventories, item lore, or equipment asynchronously (such as animated cosmetics, scoreboard/tab plugins, or custom enchantments).
3. Update ViaVersion, ProtocolLib, and any inventory/cosmetic plugins or mods to their latest versions for your Minecraft release, as older builds may trigger off-thread packet or item access.
4. If players are still getting kicked and you cannot tell which plugin or mod is modifying items off-thread, perform a binary search: temporarily remove half of your plugins/mods, test if the error stops, and repeat with the remaining half until you isolate the exact culprit.

Check your own log