The concept of null runs through programming languages. We encounter it in different forms: None, 0, NULL, nil, nullptr, undefined. All of these expressions denote the same thing: a missing or unassigned value that we are referring to. Tony Hoare (Sir Charles Antony R. Hoare), a Turing Award winner and the author of the Quicksort algorithm, described the introduction of the null reference as his “billion-dollar mistake” at OOPSLA 2009. Read more
