Found a bug in typing.py:

def to_dict(self) -> dict:
        """Return a dict mapping the property name to its definition.

        Returns:
            A JSON Schema dictionary describing the object.
        """
        type_dict = self.type_dict
        if self.optional:
            type_dict = append_type(type_dict, "null")
        if self.default:
            type_dict.update({"default": self.default})
        if self.description:
            type_dict.update({"description": self.description})
        return {self.name: type_dict}

If default is 0 it does not set the default when converted to a dict. Should be

if self.default is not None:

Hey! Would you be willing to submit an MR to fix this?

Sure, later today.