Convert Date Format (From-To) Swift 3

Convert Date Format (From-To) Swift 3

func convertDateFormat(from: String, to: String, dateString: String?) -> String? {
    let fromDateFormatter = DateFormatter()
    fromDateFormatter.dateFormat = from
    var formattedDateString: String? = nil
    if dateString != nil {
        let formattedDate = fromDateFormatter.date(from: dateString!)
        if formattedDate != nil {
            let toDateFormatter = DateFormatter()
            toDateFormatter.dateFormat = to
            formattedDateString = toDateFormatter.string(from: formattedDate!)
        }
    }
    return formattedDateString
}