If I try to pass a value of 0 for the basis prop, the FlexView will ignore that and leave the basis at auto (its default). This can also be seen on the live playground (in the interactive section at the bottom, try entering 0 as the basis).
I suspect this is happening because of an if-condition that checks the value of basis, and a value of 0 evaluates to be falsy, so the if-block acts as if no basis prop was provided. This is potentially happening in FlexView.tsx, on line 201, in the getBasis function.