protected function getStartDate()
{
$startDate = null;
$sections = SubscriptionSection::GetSubscriptionSections($this->m_dbObject->getSubscriptionId());
foreach ($sections as $section) {
$sectionStartDate = $section->getStartDate();
if ($sectionStartDate < $startDate || is_null($startDate)) {
$startDate = $sectionStartDate;
}
}
return $startDate;
}