Call to a member function format() on null

[paranoid-m]

I use laravel 5.4.
when I use sample code like this on my controller

public function index()
{
 $events = [];

$events[] = \Calendar::event(
    'Event One', //event title
    false, //full day event?
    '2015-02-11T0800', //start time (you can also use Carbon instead of DateTime)
    '2015-02-12T0800', //end time (you can also use Carbon instead of DateTime)
	0 //optionally, you can specify an event ID
);

$events[] = \Calendar::event(
    "Valentine's Day", //event title
    true, //full day event?
    new \DateTime('2015-02-14'), //start time (you can also use Carbon instead of DateTime)
    new \DateTime('2015-02-14'), //end time (you can also use Carbon instead of DateTime)
	'stringEventId' //optionally, you can specify an event ID
);

$eloquentEvent = EventModel::first(); //EventModel implements MaddHatter\LaravelFullcalendar\Event

$calendar = \Calendar::addEvents($events) //add an array with addEvents
    ->addEvent($eloquentEvent, [ //set custom color fo this event
        'color' => '#800',
    ])->setOptions([ //set fullcalendar options
		'firstDay' => 1
	])->setCallbacks([ //set fullcalendar callback options (will not be JSON encoded)
        'viewRender' => 'function() {alert("Callbacks!");}'
    ]);

return view('hello', compact('calendar'));

}

Show me this error

Call to a member function format() on null

I even install laravel 5.6 and show me error again

[jabberdog]

I have the same issue, did anyone think of a way to get around this?