reason: ‘attempt to insert row 0 into section 0, but there are only 0 rows in section 0 after the update’
`func itemDetailViewController(controller: ItemDetailViewController, didFinishAddItem item: ChecklistItem) {
let newRowIndex = checklist.items.count
items.append(item)
let indexPath = NSIndexPath(forRow: newRowIndex, inSection: 0)//crash in this line
let indexPaths = [indexPath]
tableView.insertRowsAtIndexPaths(indexPaths, withRowAnimation: .Automatic)
dismissViewControllerAnimated(true, completion: nil)
}`