App crashed when drag event

[Echoecho126]

There is a event1,which date range 09:30~ 15:30. When the view scrolled to 15:20 and the event1's top scroll out of the view, draging the event1 can lead to crash. The crash come from the method

• (BOOL)beginMovingEventOfType:(MGCEventType)type atIndexPath:(NSIndexPath*)path{
  ...
  self.interactiveCellDate =[self dateAtPoint:self.interactiveCell.frame.origin rounded:YES];// nil date cause crash。
  ...
  }