When placing a sail against a regular block all is fine but when using Create's smart extension feature (placing a sail against another sail you're shown an arrow as to where the sail will extend) to place a sail the game crashes with IllegalArgumentException: Invalid hand null.

It started for someone else on a dedicated server I host locally. Their game crashed multiple times in a row placing the sails on current or new construction. I could however show up and place the sails without any trouble. Later on I created a new SP map to test and there the same crash happened to me. Attaching crash report from single player event.

We're running CtE Dissonance version 2.9.5 through CurseForge on Windows 10.
crash-2021-05-18_20.59.11-client.txt

CalemiUtils WrenchEvent.class has a subscription to onBlockPlace event which seems to throw the "invalid hand null" IllegalArgumentException.
Decompiled the offending line reads:
final ItemStack stack = player.func_184586_b(player.func_184600_cs());
So either (likely) Create has already invalidated the player entity and not consumed the event properly or CalemiUtils is thrown first and the hidden functions on this row somehow collides when thrown from outside Creates workspace.
Given how the line is likely called as:
final ItemStack stack = player.get_item_stack(player.hand());
Or something similar I'm leaning towards the problem being on Create's side.

Create issue tracker: Creators-of-Create/Create#1614

This was apparently fixed in CalemiUtils-1.16.4.

1.16.4 is the minecraft version. I can see if calemi is up to fixing the 1.15.2 version

fixed thanks to calemi <3