Random server crash: NullPointerException in AttributeInstanceSet during world tick

[MrNickax]

Checklist

• I have searched the existing issues and the documentation
• I ticked all the boxes without actually reading them
• I am using latest Leaf build from https://www.leafmc.one/download
• I tested and couldn't replicate this issue on latest Paper or Purpur build

What behaviour is observed?

The server crashes randomly 2–3 times per day with a java.lang.NullPointerException: Exception ticking world.

The crash appears to happen during entity attribute synchronization, specifically inside AttributeInstanceSet.toArray.

What is the expected behavior?

How to reproduce?

The issue is random and hard to reproduce reliably.

Spark profiler link

https://spark.lucko.me/zDsbAZCRA9

Error log (if applicable)

https://mclo.gs/Kv1ImTs

[Dreeam-qwq]

Try to replicate without plugins, or use binary search to find the plugin that causes this issue.

[MrNickax]

I’m currently running a few servers with Leaf, and the one crashing is the Lobby server.

I checked the plugins on both servers and found only two plugins on the Lobby that aren’t on the Survival Lobby (the other Leaf server).

The first is BetterJoinSpawn, which sends players to a specific location when they join, I don’t think this one is causing the issue.

The second is ItemJoin, which gives items to players on join. If I had to guess, the crash might be happening when items are given to the player during join, but I’m not sure whether this is a Leaf issue or an ItemJoin issue.

I also tried reproducing the problem using Paper, but I wasn’t able to.

[Dreeam-qwq]

I’m currently running a few servers with Leaf, and the one crashing is the Lobby server.

I checked the plugins on both servers and found only two plugins on the Lobby that aren’t on the Survival Lobby (the other Leaf server).

The first is BetterJoinSpawn, which sends players to a specific location when they join, I don’t think this one is causing the issue.

The second is ItemJoin, which gives items to players on join. If I had to guess, the crash might be happening when items are given to the player during join, but I’m not sure whether this is a Leaf issue or an ItemJoin issue.

I also tried reproducing the problem using Paper, but I wasn’t able to.

Can you install only ItemJoin to confirm that?

[MrNickax]

That’s going to be difficult, the crash only occurs once or twice per day on a server with around 250 players, I can’t reliably reproduce it. Removing ItemJoin from the lobby wouldn’t be a viable, as players need it to access the different game modes.

[hayanesuru]

PaperMC/Paper#13639