Deleting an Edge Gateway: task completion

$sdkEdgeGateway = $service->createSDKObj($edgeGatewayRef);

$edgeGateway = $sdkEdgeGateway->getEdgeGateway();

$deleteEdgeGateway = $sdkEdgeGateway->delete();

$task = $service->waitForTask($deleteEdgeGateway);

if ($task->get_status() != 'success'){

exit("Failed to delete Edge Gateway");

}

Error:

PHP Fatal error:  Uncaught exception 'VMware_VCloud_SDK_Exception' with message 'The given object is in class VMware_VCloud_SDK_Service_Abstract type, cannot invoke refetch() function.

' in /sdk/utils/VMware/VCloud/ServiceAbstract.php:268

Or:

$task = $deleteEdgeGateway->getTasks()->getTask();

if (sizeof($task) > 0){                        $service->waitForTask($task[0]);

}    

Or:

$task = $edgeGateway->getTasks()->getTask();

if (sizeof($task) > 0){                        $service->waitForTask($task[0]);

}

Error:

PHP Fatal error:  Call to a member function getTasks() on null