Server Crash (NPE) when placing blocks on a Contraption at a Train Station

[Cha-Shao]

Context

Description

A java.lang.NullPointerException occurs when interacting with a Create contraption (specifically by placing a torch or updating blocks) while using the Sable physics mod. The crash is triggered during the entity ticking process.

Technical Details

• Minecraft Version: 1.21.1
• NeoForge Version: 21.1.227
• Sable Version: 1.1.3
• Create Version: 6.0.10
• Error Type: java.lang.NullPointerException
• Error Message: Cannot invoke "org.joml.Vector3dc.negate(org.joml.Vector3d)" because the return value of "dev.ryanhcode.sable.api.physics.mass.MassTracker.getCenterOfMass()" is null

Steps to Reproduce

1. Set up a Create Train Station and assemble a train/contraption.
2. Place a Torch (or any block that updates the contraption structure) on the assembled contraption.
3. The server immediately crashes when the AbstractContraptionEntity attempts to tick and update its physical properties via Sable's Mixin.

Analysis

The crash occurs in com.simibubi.create.content.contraptions.AbstractContraptionEntity.sable$buildProperties. Sable's mass tracking system fails to return a valid center of mass (getCenterOfMass() returns null), causing the physics calculation to fail when it attempts to negate that vector.

Environment

• OS: Linux (amd64) version 6.1.0-44-amd64
• Java: 21.0.10 (Eclipse Adoptium)
• Affected Entity: minecraft:minecart (Entity ID: 7) carrying an OrientedContraptionEntity

Crash Report

https://mclo.gs/0RXjAHK