In Indonesia, many Javanese people traditionally have only one name. When they migrate to countries like Singapore, where a surname is required, they often use their given name as both their first and last name. As a result, you may see names such as Chandra Chandra or Supardi Supardi.
Nowadays the Indonesian law requires at least two words for the person's full name, and the full name is regarded as a single entity no matter how many words it contains. Older generations of Javanese, having only a single name, usually duplicate it - I have seen such duplicate names in official Indonesian documents.
Or you get something like Someone FNU. Where FNU at some point meant 'first name unknown', but is now the person's last name at least in the people I've known... But I see references to it ending up as their firstname, so FNU Someone, which would make a little more sense, but is still pretty bizarre. Someone Someone seems like the best way to handle it, assuming single names aren't allowed (because yeah)
