getHangoutLink() returns null character instead of empty string

[nagaihiroki-git]

Environment details

• OS: Linux
• PHP version: 8.2
• Package name and version: google/apiclient v2.18.2

Steps to reproduce

1. Create a Google Calendar service instance
2. Attempt to get an event using events->get() method
3. Try to access the Hangout link using getHangoutLink()
4. Observe that getHangoutLink() returns a null character instead of an empty string

Code example

$service = $this->createGoogleService();
$event = $service->events->get($calendarId, $eventId);

// Debug output showing the issue
echo 'shouldGenMeetingUrsssl: ' . ($event->getHangoutLink() !== "") . "\n"; // false
echo 'shouldGenMeetingUrl: ' . $event->getHangoutLink() . "\n"; // 
echo 'isNULL: ' . ($event->getHangoutLink() === null) . "\n"; // true
echo 'isEmptyString: ' . ($event->getHangoutLink() === "") . "\n"; //false

Expected behavior

The getHangoutLink() method should return an empty string ("") when no Hangout link is present, according to the API documentation.

Actual behavior

The getHangoutLink() method returns a null character (\0), not an empty string ("") or PHP null value. This causes unexpected behavior with string comparisons and can lead to subtle bugs in string handling code.