Test if there is no document for resource.

        :param resource: resource name

def is_empty(self, resource):
        """Test if there is no document for resource.

        :param resource: resource name
        """
        args = self._es_args(resource)
        res = self.elastic(resource).count(body={'query': {'match_all': {}}}, **args)
        return res.get('count', 0) == 0