Why are zero errors called "errors per million"?

Errors related to null values (null) are often called "Million Dollar Mistakes" because of their high likelihood of occurrence in programs that use type systems with implicit null resolution. Fil Hower, the inventor of null in the Algol W language, later called it his "Million Dollar Mistake," leading to countless NullPointerExceptions and other issues caused by unexpected null values at runtime. Flutter/Dart, starting from version 2.12 with Null Safety enabled, actively combats this problem by forcing developers to handle potential null values at compile time, significantly reducing the likelihood of such errors at runtime.