Applying `typingAttributes` whilst firstResponder on a UITextField

FunTimesWithUITextField.swift

textField.text = "fred"

textField.becomeFirstResponder()
DispatchQueue.main.async {
  // Set some typingAttributes
  self.textField.typingAttributes = [NSAttributedStringKey.font.rawValue: UIFont.boldSystemFont(ofSize: 18)]
  
  // Resign first responder
  self.textField.resignFirstResponder()
  DispatchQueue.main.async {
    self.textField.text = "bob" // 💥 Crash on iOS 10 and below
  }
}

/* Stack trace
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** setObjectForKey: object cannot be nil (key: NSParagraphStyle)'
*** First throw call stack:
(
	0   CoreFoundation                      0x0000000103aeeb0b __exceptionPreprocess + 171
	1   libobjc.A.dylib                     0x0000000100cea141 objc_exception_throw + 48
	2   CoreFoundation                      0x0000000103a09682 -[__NSDictionaryM setObject:forKey:] + 1042
	3   UIKit                               0x0000000101444f00 -[UILabel _setLineBreakMode:] + 219
	4   UIKit                               0x0000000101cc3710 -[UITextField _updateTextLabel] + 513
	5   UIKit                               0x0000000101cc46de -[UITextField setText:] + 221
	6   defaultTextAttributes               0x000000010070fad7 _T021defaultTextAttributes14ViewControllerC11viewDidLoadyyFyycfU_yycfU_ + 279
	7   defaultTextAttributes               0x0000000100710b7d _T021defaultTextAttributes14ViewControllerC11viewDidLoadyyFyycfU_yycfU_TA + 13
	8   defaultTextAttributes               0x000000010070fb2d _T0Ieg_IeyB_TR + 45
	9   libdispatch.dylib                   0x0000000104a174a6 _dispatch_call_block_and_release + 12
	10  libdispatch.dylib                   0x0000000104a4005c _dispatch_client_callout + 8
	11  libdispatch.dylib                   0x0000000104a2140b _dispatch_main_queue_callback_4CF + 411
	12  CoreFoundation                      0x0000000103ab3909 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
	13  CoreFoundation                      0x0000000103a79ae4 __CFRunLoopRun + 2164
	14  CoreFoundation                      0x0000000103a79016 CFRunLoopRunSpecific + 406
	15  GraphicsServices                    0x00000001059faa24 GSEventRunModal + 62
	16  UIKit                               0x00000001011bc134 UIApplicationMain + 159
	17  defaultTextAttributes               0x00000001007118f7 main + 55
	18  libdyld.dylib                       0x0000000104a8c65d start + 1
	19  ???                                 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
*/