FullCalendar2 - retrieving delta Output in event - eventResize

I need help in this error, since when I debugged the screen action FullCalendarEventResize, it just refreshes the page and I wonder if it has error. I checked in the service studio and the error is here. 

Here is the implementation of the resize function, 

Community GuidelinesBe kind and respectful, give credit to the original source of content, and search for duplicates before posting.