Design patterns·Functional ideas that went mainstream
the type says the value might not be there, so you cannot use it without saying what happens when it is not.
Option type
Also calledMaybe, Optional, nullable type
A type with two cases — a value or nothing — making absence explicit and forcing the caller to handle it. It is the type-system answer to the null reference, and it differs from a null object in being visible rather than invisible: an option makes the caller decide, a null object silently does nothing. Its cost is ceremony in a language without pattern matching or a decent option API.