Try to release a connection. If an exception is hit, log and return
        the error string.

def _safe_release_connection(self):
        """Try to release a connection. If an exception is hit, log and return
        the error string.
        """
        try:
            self.adapter.release_connection()
        except Exception as exc:
            logger.debug(
                'Error releasing connection for node {}: {!s}\n{}'
                .format(self.node.name, exc, traceback.format_exc())
            )
            return dbt.compat.to_string(exc)

        return None