Automatic breaking of cobble to gravel? That's hard. Tricky only since vanilla doesn't have a block placer. As outlined by that crash log, some thing went Mistaken while trying to spawn a mob. Unfortunately it does not have sufficient facts for me to track down who was answerable for it, https://andreeseqc.angelinsblog.com/33247475/how-much-you-need-to-expect-you-ll-pay-for-a-good-copyright-parfum