Free runtime check of what? The point is that if nulls don't exist, there is no need for a "check". Runtime or otherwise. If I write a type that models Foo, I w

Free runtime check of what? The point is that if nulls don't exist, there is no need for a "check". Runtime or otherwise. If I write a type that models Foo, I want it to model Foo and not "Foo or null". If I want to model "Foo or no data" then I use a separate type that makes my intention clear (in Rust spelled `Option<Foo>`). Languages where nothing is precisely Foo and everything is "oh by the way this is only possibly Foo" are deeply, deeply flawed.