def METHOD_NAME(self, organization) -> str | None:
    # if a member has user_email=None, then they have yet to accept an invite
    org_owners = organization.get_members_with_org_roles(
        roles=[roles.get_top_dog().id]
    ).exclude(Q(user_email=None) | Q(user_email=""))
    def _get_email_domain(email: str) -> str | None:
        try:
            domain = Address(addr_spec=email).domain
        except Exception:
            return None
        return domain
    owner_email_domains = {_get_email_domain(owner.user_email) for owner in org_owners}
    # all owners have the same email domain
    if len(owner_email_domains) == 1:
        return owner_email_domains.pop()
    return None