[BUG] Crash during client init related to ItemColors / iron_backpack

[Kotane-TMKT]

Minecraft Version

1.21.1

Mod Version

neoforge-21.1.2

Mod Loader

Neoforge

Reproduction Steps

Install and launch several mods simultaneously.
(There are multiple patterns where each mod is independent of the others, including some I don't remember, but the ones I'm recently aware of are:
Sodium
PuzzlesLib
Age of Steam without ARLib (yes, Since there are lack of dependencies, it naturally won't be able to start on its own. However, if you install yyzsbackpack into Minecraft in that state, the crash will occur earlier and the stack trace will also change.)

Expected Behavior

The game starts up.

Actual Behavior

The game don't starts up.

Logs/Screenshots

bottom of this report (Due to exceeding the character limit, the log file is attached)

Additional Context

Bug report: crash during client init related to ItemColors / iron_backpack

Hello,

I encountered a client crash that appears to be related to yyzsbackpack during startup.

Environment

• Minecraft: 1.21.1
• NeoForge: 21.1.219

What happens

• The game crashes during client initialization.
• This seems to happen when other mods are present, but from the crash log it looks like the actual crash occurs inside yyzsbackpack’s ItemColors handling.

Relevant part of the crash

• Trying to access unbound value: ResourceKey[minecraft:item / yyzsbackpack:iron_backpack]
• NullPointerException: Trying to access unbound value...

Stack trace points to

• net.neoforged.neoforge.registries.DeferredHolder.value
• yyzsbackpack.item.ItemHandler.get
• yyzsbackpack.mixin.ItemColorsMixin
• net.minecraft.client.color.item.ItemColors.createDefault

My guess

• yyzsbackpack:iron_backpack may be accessed before it is fully bound/registered.
• So this may be an initialization-order issue that only becomes visible depending on what other mods are installed.

I have attached the crash log.

Thank you.

[Due to exceeding the character limit, the log file is attached here.]
crash-2026-03-18_10.27.40-client.txt

[Kotane-TMKT]

Postscript/Rewrite

I found a crash involving yyzsbackpack that seems worth reporting.

In my case, the original issue was that Age of Steam was installed without its required dependency, ARLib.
After installing ARLib, the game started normally.

However, before that was fixed, the client crashed in a way that pointed to yyzsbackpack first, instead of clearly surfacing the missing dependency as the primary problem.

Environment

• Minecraft: 1.21.1
• NeoForge: 21.1.219

Situation

• Age of Steam was present
• ARLib was missing
• yyzsbackpack was also installed

Observed behavior

• The game crashed during client initialization
• The crash log pointed to yyzsbackpack, especially its ItemColors handling
• After installing ARLib, the crash no longer occurred

Why I am reporting this

I understand that the setup was invalid because ARLib was missing.

Still, it seems notable that under this condition, yyzsbackpack crashes first with:

• Trying to access unbound value: ResourceKey[minecraft:item / yyzsbackpack:iron_backpack]

and the stack trace points to:

• net.neoforged.neoforge.registries.DeferredHolder.value
• yyzsbackpack.item.ItemHandler.get
• yyzsbackpack.mixin.ItemColorsMixin
• net.minecraft.client.color.item.ItemColors.createDefault

So even though the root cause was a missing dependency in another mod, yyzsbackpack appears to access its item too early and produces a misleading crash.

Also, I have seen other cases where yyzsbackpack appeared to conflict in a similar way with mods unrelated in functionality, so this may still indicate an initialization-order issue on the yyzsbackpack side.

I am attaching the crash log in case this is useful.

Thank you.

[yyz729]

it still happen in the new version?