Modding Help Modded Merchant not letting me buy things for 0 pixels

I'm making a modded merchant that sells every block in the game, when I finally finished and tried to test it I realized I can't buy anything i made another mod too and realized that I only couldn't buy things worth 0 pixels, can anybody help me with this?? the only thread I could find on this is from 2015 and it looks like this is a bug for merchants found on planets in the vanilla game

 

I ended up making a mod that makes every block in the game sellable it took me like 6 hours