Thread 1: Fatal error: cannot increment beyond endIndex

[Yancerva]

in the simulator works fine, but in the devices appear in this line the error:

subscript (r: Range<Int>) -> String {
    let start = index(startIndex, offsetBy: r.lowerBound)
    let end = index(startIndex, offsetBy: r.upperBound) <- Thread 1: Fatal error: cannot....
    return String(self[Range(start ..< end)])
}