UDID migration for unique identifier within a specific app

UDIDMigration.m

NSString *UUID = [[NSUserDefaults standardUserDefaults] objectForKey:kApplicationUUIDKey];
    
if (!UUID) {
  CFUUIDRef uuid = CFUUIDCreate(NULL);
  UUID = (__bridge_transfer NSString *)CFUUIDCreateString(NULL, uuid);
  CFRelease(uuid);

  [[NSUserDefaults standardUserDefaults] setObject:UUID forKey:kApplicationUUIDKey];
  [[NSUserDefaults standardUserDefaults] synchronize];
}