docs: def _validate_type(self):  # type: () -> None
          """Validation to ensure value is the correct type"""
          if not isinstance(self._value, self._type):
              title = '{} has an invalid type'.format(self._key_name())
              description = '{} must be a {}'.format(self._key_name(), self._type.__name__)
  
              self._add_error(title=title, description=description)