> The logic-variant of Null usage for "unknown" "missing" "invalid" values is unavoidable in programming. This is why that null concept shows up repeatedly in different forms such as NaN in floating point, NULL in SQL language, etc

As an aside here, there is also a school of thought that NULL in SQL was a mistake, see e.g. https://www.dcs.warwick.ac.uk/~hugh/TTM/Missing-info-without... and http://thethirdmanifesto.com/ (Hugh Darwen and Chris Date)