Get the DB session associated with the task (open a new one if necessary)

        Returns:
            sqlalchemy.orm.session.Session: DB session

def session(self):
        """Get the DB session associated with the task (open a new one if necessary)

        Returns:
            sqlalchemy.orm.session.Session: DB session
        """
        if self._session is None:
            self._session = self.client.create_session()

        return self._session