Pantheon\Terminus\Collections\OrganizationSiteMemberships::getSite PHP Method

    public function getSite($site_id)
    {
        if (is_null($membership = $this->get($site_id))) {
            throw new TerminusException('This user is not a member of an organization identified by {id}.', ['id' => $site_id]);
        }
        return $membership->getSite();
    }