FIX Notice: Undefined property: page

Test:
<code>
$tracker = new UnitedPrototype\GoogleAnalytics\Tracker($ua, $host);
$visitor = new UnitedPrototype\GoogleAnalytics\Visitor();
$visitor->setIpAddress($_SERVER['REMOTE_ADDR']);
$visitor->setUserAgent($_SERVER['HTTP_USER_AGENT']);
$session = new UnitedPrototype\GoogleAnalytics\Session();
$event = new UnitedPrototype\GoogleAnalytics\Event();
 // Required:
 $event->setCategory('category');
 $event->setAction('action');
      
 // Optional:
 $event->setLabel('label');
 $event->setValue(1);

 $tracker->trackEvent($event, $session, $visitor);

Error (Notice): 

UnitedPrototype\GoogleAnalytics\Internals\Request\EventRequest::$page in UnitedPrototype\GoogleAnalytics\Internals\Request\EventRequest->buildParameters() (line 91 of /{my_site}/sites/all/libraries/php-ga/src/GoogleAnalytics/Internals/Request/EventRequest.php).

</code>