Calendar Server Error when trying to Create an Event per click in Calendar

[Freelancer]

Seems to be associated with the other Bug Report (Create Event per Click in Calendar does not respect Language Settings)... When I try to create an event per clicking in the calendar it shows the popup and when saving the event, the following server error appears:

Error Info
Call to a member function format() on boolean - library/NixFifty/Calendar/ControllerPublic/Event.php:346

Stack Trace
#0 /Applications/XAMPP/xamppfiles/htdocs/forum/library/XenForo/FrontController.php(369): NixFifty_Calendar_ControllerPublic_Event->actionQuickSave()
#1 /Applications/XAMPP/xamppfiles/htdocs/forum/library/XenForo/FrontController.php(152): XenForo_FrontController->dispatch(Object(XenForo_RouteMatch))
#2 /Applications/XAMPP/xamppfiles/htdocs/forum/index.php(13): XenForo_FrontController->run()
#3 {main}

Request State
Array
(
    [url] => http://localhost/forum/events/0/quick-save
    [_GET] => Array
        (
        )

    [_POST] => Array
        (
            [event_title] => Test Event
            [start_date] => 2018-07-08
            [start_time] => 1:30am
            [end_date] => 2018-07-09
            [end_time] => 2:00am
            [event_timezone] => Europe/Amsterdam
            [_xfToken] => ********
            [_xfRequestUri] => /forum/events/
            [_xfNoRedirect] => 1
            [_xfResponseType] => json
        )

)