def METHOD_NAME(self, org):
    # Given an org, work out the start date for a new division set
    # based on the end date of the most recent previous division set
    divsets = OrganisationDivisionSet.objects.filter(organisation=org)
    if not divsets:
        raise Exception(
            "Could not find any previous DivisionSets for Organisation %s"
            % org
        )
    if not divsets.latest().end_date:
        raise Exception(
            "End date for previous DivisionSets %s is NULL" % divsets[0]
        )
    return divsets.latest().end_date + datetime.timedelta(days=1)