This is a concern, but the advantage to Maybe is it makes this concern very explicit. SML/NJ code will not compile if you don't have a binding to handle the Non

This is a concern, but the advantage to Maybe is it makes this concern very explicit. SML/NJ code will not compile if you don't have a binding to handle the None for an option 'a type. The programmer does of course then have the option of doing None => raise Error but practically speaking, when deciding it's time to make your code more robust, it's a lot easier to text search for instances of "None => raise" than to search for the absence of proper handling of the possibility of a null arg or return value.