Get a JSON compatible value

def json_data(self, instance, default=None):
        """Get a JSON compatible value
        """
        value = self.get(instance)

        out = []
        for rel in value:
            if rel.isBroken():
                logger.warn("Skipping broken relation {}".format(repr(rel)))
                continue
            obj = rel.to_object
            out.append(api.get_url_info(obj))
        return out