Get a :class:`Issue` by ref.

        :param ref: :class:`Issue` reference

def get_issue_by_ref(self, ref):
        """
        Get a :class:`Issue` by ref.

        :param ref: :class:`Issue` reference
        """
        response = self.requester.get(
            '/{endpoint}/by_ref?ref={us_ref}&project={project_id}',
            endpoint=Issue.endpoint,
            us_ref=ref,
            project_id=self.id
        )
        return Issue.parse(self.requester, response.json())