Crashing bug with DateComponentsFormatter on iOS 12

gistfile1.txt

When called during launch with nil calendar and abbreviated units, DateComponentsFormatter.string(from:)
crashes attempting to call -[__NSCFString locale].

Area:
Foundation

Summary:

Due to rdar://problem/44835278 we're using DateComponentsFormatter with its calendar property set to nil
to force it to use the en_US_POSIX locale, since we can't set the locale directly. The unitsStyle
property is .abbreviated. This generally works, however it crashes consistently when calling 
string(from: TimeInterval) during launch, unrecognized selector -[__NSCFString locale].

Steps to Reproduce:

An example project is included for you to run and observe the crash. You can execute the following code in
any app's didFinishLaunching app delegate method:

        let duration: TimeInterval = 30_000
        let formatter = DateComponentsFormatter()
        formatter.calendar = nil
        formatter.unitsStyle = .abbreviated
        let abbreviated = formatter.string(from: duration)!
        print(abbreviated)

Expected Results:

No crash. Returns a string.

Actual Results:

Crash.

Version/Build:

iOS 12.1.3 (16D39)

Configuration:

iPhone 7 Plus and the iPhone 8 simulator

----

I just tried something slightly different in my code (not initializing the formatter in a static let property)
and this time it crashed sending the locale selector to BSActionListenerToken instead of __NSCFString, so
there might be a race or something more interesting with memory going on here.