[Crash Report] Server crash when npc entity try to defend player from mob

[NantaArthur123]

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Minecraft and Mod version 🐞 1.21 newest easy npc on fabric

Description of the crash 💥 Make new npc that defend your base, and suddenly crash when hitting zombie

Steps to reproduce the crash ⚙️

1. Add new npc
2. Give modded bow on mainhand and arrow on offhand
3. Tell the npc to shoot mob, and crash

Expected behavior before the crash ✔️ A clear and concise description of what you expected to happen before the crash occurred.

Logs 📝 Highlighted log before crash

[18:27:22] [Server thread/ERROR]: Exception stopping the server
net.minecraft.class_148: Saving entity NBT
        at net.minecraft.class_1297.method_5647(class_1297.java:1940) ~[server-intermediary.jar:?]
        at net.minecraft.class_1297.method_5786(class_1297.java:1858) ~[server-intermediary.jar:?]
        at net.minecraft.class_1297.method_5662(class_1297.java:1866) ~[server-intermediary.jar:?]
        at net.minecraft.class_5565.method_31734(class_5565.java:109) ~[server-intermediary.jar:?]
        at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1708) ~[?:?]
        at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:762) ~[?:?]
        at net.minecraft.class_5565.method_31760(class_5565.java:107) ~[server-intermediary.jar:?]
        at net.minecraft.class_5579.method_31812(class_5579.java:299) ~[server-intermediary.jar:?]
        at net.minecraft.class_5579.method_31837(class_5579.java:316) ~[server-intermediary.jar:?]
        at net.minecraft.class_5579.method_31842(class_5579.java:394) ~[server-intermediary.jar:?]
        at it.unimi.dsi.fastutil.longs.LongCollection.removeIf(LongCollection.java:274) ~[fastutil-8.5.12.jar:?]
        at net.minecraft.class_5579.method_31836(class_5579.java:392) ~[server-intermediary.jar:?]
        at net.minecraft.class_3218.method_14176(class_3218.java:823) ~[server-intermediary.jar:?]
        at net.minecraft.server.MinecraftServer.method_3723(MinecraftServer.java:556) ~[server-intermediary.jar:?]
        at net.minecraft.server.MinecraftServer.method_3782(MinecraftServer.java:620) ~[server-intermediary.jar:?]
        at net.minecraft.class_3176.method_3782(class_3176.java:561) ~[server-intermediary.jar:?]
        at net.minecraft.server.MinecraftServer.method_29741(MinecraftServer.java:735) ~[server-intermediary.jar:?]
        at net.minecraft.server.MinecraftServer.method_29739(MinecraftServer.java:281) ~[server-intermediary.jar:?]
        at java.base/java.lang.Thread.run(Thread.java:1583) [?:?]
Caused by: java.lang.IllegalStateException: Cannot encode empty ItemStack
        at net.minecraft.class_1799.method_57358(class_1799.java:401) ~[server-intermediary.jar:?]
        at net.minecraft.class_1665.method_5652(class_1665.java:541) ~[server-intermediary.jar:?]
        at net.minecraft.class_1297.method_5647(class_1297.java:1922) ~[server-intermediary.jar:?]
        ... 18 more

Server Logs: https://mclo.gs/UlhUMOq

Additional context 📋 Add any other context or information about the crash here.

[MarkusBordihn]

Thank you for the report. Currently, crossbows, bows, and guns each use their own specific ammunition, so the off-hand slot isn't utilized in these cases.

This issue should be resolved in version 5.5.2, which will go live within the next few hours.

[NantaArthur123]

Thank you for the report. Currently, crossbows, bows, and guns each use their own specific ammunition, so the off-hand slot isn't utilized in these cases.

This issue should be resolved in version 5.5.2, which will go live within the next few hours.

can I ask what is guns type weapon?