Blender Version
Broken: 2.81 HEAD/master (dfaaf50538c)
Worked: 2.80 (release version at least)

Short description of error
Crash (assert) when sculpting with curve stroke.

Exact steps for others to reproduce the error
Go to sculpt mode and change Stroke to Curve (from Space)

OR open:

And start sculpting. You will soon run into:

BLI_assert failed: //source/blender/blenkernel/intern/undo_system.c:455, BKE_undosys_step_push_init_with_type(), at 'ustack->step_init == ((void *)0)'

Full backtrace: P1160