According to Apple docs, dequeReusableCellWithIdentifier returns an optional value :
func dequeueReusableCellWithIdentifier(_ identifier: String) -> UITableViewCell?
But in your code, you explicitly unwrap this value because your cell object is an UITableViewCell object.
You should use - dequeueReusableCellWithIdentifier:forIndexPath: : its return value is not optional thus you don't have to unwrap your cell.