ios - DateFormatter doesn't return date for "HH:mm:ss"

Question

Here is the code excerpt:

func mapping(map: Map) {
    time      <- (map["time"], TransformOf<Date, String>(fromJSON: {
        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "HH:mm:ss"
        //dateFormatter.timeZone = TimeZone(abbreviation: "EEST")
        if let argument = $0 {
            let date = dateFormatter.date(from: argument)
            return dateFormatter.date(from: argument)
        }
        return nil
        }}

$0 is string with "22:12:00". I put "let date" to see what it returns and it's nil. I've looked up for format codes here: http://waracle.net/iphone-nsdateformatter-date-formatting-table/

Code should work actually. What am I doing wrong?

EDIT: Added the whole function

EDIT2: I just noticed it's working properly on iPhone 7 iOS 10.1 simulator but returns nil on my iPod 10.1.1 (2016). This is so weird.

Answer 1

From Technical Q&A QA1480 –?NSDateFormatter and Internet Dates (emphasis added):

On the other hand, if you're working with fixed-format dates, you should first set the locale of the date formatter to something appropriate for your fixed format. In most cases the best locale to choose is "en_US_POSIX", a locale that's specifically designed to yield US English results regardless of both user and system preferences.

This will prevent the date from being interpreted according to the user's regional settings:

let dateFormatter = DateFormatter()
// Set the locale first ...
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
// ... and then the date format:
dateFormatter.dateFormat = "HH:mm:ss"

// ...

See also What is the best way to deal with the NSDateFormatter locale "feechur"?.