{'type': 'boolean'}

def _validate_nullable(self, nullable, field, value):
        """ {'type': 'boolean'} """
        if value is None:
            if not nullable:
                self._error(field, errors.NOT_NULLABLE)
            self._drop_remaining_rules(
                'allowed',
                'empty',
                'forbidden',
                'items',
                'keysrules',
                'min',
                'max',
                'minlength',
                'maxlength',
                'regex',
                'schema',
                'type',
                'valuesrules',
            )