Help with jigsaws please

I'm getting an error when I try to generate a custom jigsaw that spawns in random brewing stands with potions:


[10:58:17] [Server thread/ERROR]: No starting jigsaw minecraft:empty found in start pool minecraft:igloo/shelf


Anyone know how to fix this error? I just want to generate a single brewing stand with different potions in it OR a cake. I have a huge loot pool.
Continue to help post