public function removeMember($contactId, $sourceId = null)
{
$members = @unserialize($this->attributes['__members']);
if (is_null($sourceId) || $sourceId == $this->getSource()) {
$i = array_search($contactId, $members);
} else {
$i = array_search($sourceId . ':' . $contactId, $members);
}
if ($i !== false) {
unset($members[$i]);
}
$this->attributes['__members'] = serialize($members);
return true;
}