app crash on numberOfItemsInSection method of EPCalendarPicker class in swift 3.0.
crash logs reason: 'the collection view's data source did not return a valid cell from -collectionView:cellForItemAtIndexPath: for index path <NSIndexPath: 0xc000000000000016> {length = 2, path = 0 - 0}'
app crash on numberOfItemsInSection method of EPCalendarPicker class in swift 3.0. crash logs reason: 'the collection view's data source did not return a valid cell from -collectionView:cellForItemAtIndexPath: for index path <NSIndexPath: 0xc000000000000016> {length = 2, path = 0 - 0}'