def METHOD_NAME(campaign_name: str) -> None:
    """
    Raises an exception if the given follow-up campaign name doesn't exist, e.g.:
        >>> ensure_followup_campaign_exists('BOOP')
        Traceback (most recent call last):
        ...
        AttributeError: 'Settings' object has no attribute 'RAPIDPRO_FOLLOWUP_CAMPAIGN_BOOP'
    Note that this will *not* raise anything if the campaign exists but
    has not been configured.
    """
    DjangoSettingsFollowupCampaigns.get_campaign(campaign_name)