fix(caldav): test for null and blank value

Signed-off-by: SebastianKrupinski <krupinskis05@gmail.com>

apps/dav/lib/CalDAV/Reminder/ReminderService.php

@@ -847,7 +847,7 @@ class ReminderService {
 	private function getCalendarTimeZone(int $calendarid): DateTimeZone {
 		$calendarInfo = $this->caldavBackend->getCalendarById($calendarid);
 		$tzProp = '{urn:ietf:params:xml:ns:caldav}calendar-timezone';
-		if (!isset($calendarInfo[$tzProp])) {
+		if (empty($calendarInfo[$tzProp])) {
 			// Defaulting to UTC
 			return new DateTimeZone('UTC');
 		}

apps/dav/tests/unit/CalDAV/Reminder/ReminderServiceTest.php

@@ -427,7 +427,7 @@ EOD;
 		$this->reminderService->onCalendarObjectCreate($objectData);
 	}
 
-	public function testOnCalendarObjectCreateAllDayWithoutTimezone(): void {
+	public function testOnCalendarObjectCreateAllDayWithNullTimezone(): void {
 		$objectData = [
 			'calendardata' => self::CALENDAR_DATA_ALL_DAY,
 			'id' => '42',
@@ -454,6 +454,33 @@ EOD;
 		$this->reminderService->onCalendarObjectCreate($objectData);
 	}
 
+	public function testOnCalendarObjectCreateAllDayWithBlankTimezone(): void {
+		$objectData = [
+			'calendardata' => self::CALENDAR_DATA_ALL_DAY,
+			'id' => '42',
+			'calendarid' => '1337',
+			'component' => 'vevent',
+		];
+		$this->timeFactory->expects($this->once())
+			->method('getDateTime')
+			->with()
+			->willReturn(DateTime::createFromFormat(DateTime::ATOM, '2023-02-03T13:28:00+00:00'));
+		$this->caldavBackend->expects(self::once())
+			->method('getCalendarById')
+			->with(1337)
+			->willReturn([
+				'{urn:ietf:params:xml:ns:caldav}calendar-timezone' => '',
+			]);
+
+		// One hour before midnight relative to the server's time
+		$expectedReminderTimstamp = (new DateTime('2023-02-03T23:00:00'))->getTimestamp();
+		$this->backend->expects(self::once())
+			->method('insertReminder')
+			->with(1337, 42, self::anything(), false, 1675468800, false, self::anything(), self::anything(), 'EMAIL', true, $expectedReminderTimstamp, false);
+
+		$this->reminderService->onCalendarObjectCreate($objectData);
+	}
+
 	public function testOnCalendarObjectCreateAllDayWithTimezone(): void {
 		$objectData = [
 			'calendardata' => self::CALENDAR_DATA_ALL_DAY,