docs: def certify_bool(value, required=True):
      """
      Certifier for boolean values.
  
      :param value:
          The value to be certified.
      :param bool required:
          Whether the value can be `None`.  Defaults to True.
      :raises CertifierTypeError:
          The type is invalid
      """
      if certify_required(
          value=value,
          required=required,
      ):
          return
  
      if not isinstance(value, bool):
          raise CertifierTypeError(
              message="expected bool, but value is of type {cls!r}".format(
                  cls=value.__class__.__name__),
              value=value,
              required=required,
          )