Dispenser (up/down facing) attempting to summon wither crashes the server

Hey there,

I discovered a bug which is present in at least 1.13 and the latest snapshot (18w32a) which will crash the server(SMP)/client(SP).

The problem exists with dispensers attempting to summon a wither (only happens if there is a valid wither soul sand body) but only if the dispensers are facing up or down.

If you were to put a clock onto the dispenser (in a spawn chunk) it will render the map completely useless unless you have a backup or the bug is fixed (or mcedit supports 1.13) hence why I posted this as a private bug.

Cheers,
Chaos

Video demonstration: https://www.youtube.com/watch?v=q9gxgsUskwc

 

Update: The problem does NOT apply for snowmen or iron golems, only the wither.