def METHOD_NAME(res: LibresFacade, obs_keys: List[str]) -> Optional[str]:
    summary_obs = res.get_observations().getTypedKeylist(
        EnkfObservationImplementationType.SUMMARY_OBS
    )
    for key in obs_keys:
        _, observation = res.get_observations().get_dataset(key)
        if key in summary_obs:
            return observation.name.values.flatten()[0]
        return key
    return None