I've been programming for over a quarter century, and I feel pretty confident that I've never written anything that could confuse 'null' with NULL. I can't even think of a language that would let you easily do this. If web forms aren't accepting NULL, then somebody probably specifically programmed the word 'null' into a filter of disallowed entries. Probably to stop clerks from entering the word 'null' to mean empty…
Object a = null;
String s = "foo bar " + a; // s == "foo bar null"
So, it's possible to get "null" as a string downstream, when some variable that should be non-nulleable - was null. If you find such a bug and incompetently fix it by checking for "null" downstream instead of checking before turning variables into strings - you have the error from the article. Especially if you check ignoring the case.BTW guess how I know it's working like that :)