Free shipping if weight is not defined

I’m having the same problem. If the weight is not set in product details then shipping is free. I think this is not correct, because it is possible that you forget to enter the shipping weight or you don’t want to enter it. It would be more logical when shipping is not set the weight will be 0 grams or whatever unit you are using for weight, so shipping of this product will be calculated using the lowest weight categorie.

Hope you can help…