MBCommandNerd

Update: I just discovered that the same exact thing happens when colliding head-on with a block while flying with an Elytra propelled by firework rockets. It appears to be an issue regarding ALL fast-moving entity collisions–at least from what I can tell.

I have also experienced this issue on 1.21.4, in a private LAN world hosted by my dad in the other room. Whenever I throw a Wind Charge (regardless of where I got the Wind Charge items from or my physical location in the world) and it hits anything, the game instantly crashes. I have attached the crash report generated automatically by the game, as well as the exit code information below.
The game crashed whilst unexpected error
Error: java.lang.NullPointerException: Unexpected error
Exit Code: -1

I just noticed this happening in 19w44a, the latest snapshot of 1.15. Still not fixed yet, apparently. I managed to get a video of it happening, and I've attached it to this comment. Hope this helps!