code: def _set_slots_to_null(self, cls):
          
          if hasattr(cls, "__slots__"):
              for s in cls.__slots__:
                  self.__setattr__(s, Null)
          for b in cls.__bases__:
              self._set_slots_to_null(b)
docs: WHY ARE SLOTS NOT ACCESIBLE UNTIL WE ASSIGN TO THEM?