protected function getExpirationDate()
{
$expirationDate = null;
$sections = SubscriptionSection::GetSubscriptionSections($this->m_dbObject->getSubscriptionId());
foreach ($sections as $section) {
$sectionExpDate = $section->getExpirationDate();
if ($sectionExpDate > $expirationDate) {
$expirationDate = $sectionExpDate;
}
}
return $expirationDate;
}