Crash-Report: https://paste.dimdev.org/etapebaduc.mccrash
Player Weight: 1.4
Forge: 14.23.5.2815

good that it is solved.

I know this sounds weird but this is not Playerweights issue since it only gets the Inventory via Forges Capabilities, which is basically overrideable by anything with ASM. I have no control over that.

Sry but some other mod causes that i get wrong information. I Even check if a mod would throw in a Null Inventory since that is a possiblity, but someone dropped in a Inventory Wrapper with a nullObject, which my system can not detect (and is also impossible to detect in all scenarios)

Could a Mod like Astikor Carts could cause something like this? because every time i try to sit on a cart the game crashes with the error shown above.
https://minecraft.curseforge.com/projects/astikorcarts

Thank you for reporting this, it is indeed an issue on my end within AstikorCarts.
I will investigate and should be able to fix it soon. For now, you will have to play without AstikorCarts.