Variation quantity

Hello,

I would like to put “0” in my options in variation quantity automaticaly instead a null value:
https://i.gyazo.com/2ba9ba862c4f9e843ec32736fe7d55f6.png
Because if there is not a “0” it generates this error:
https://i.gyazo.com/32e1c0ab03f330c92dc4cee6ba115d97.png

The URL of my website: https://camisetasmartorell.com/producto/camiseta-algodon-impresa-todo-color/