Null

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Null

It indicates the absence of a value. If you call a method that doesn’t return anything and get its returned value, you get null back. The null data type is also used to initialize uninitialized variables with a default value.

    class Newton {
        var mass = 10;
        var acceleration;
        func force() {
            return mass * acceleration;
        }
    }

    func f2() {
        var sir = Newton();
        // acceleration instance variable has no default value
        // so it is automatically set to null
        return sir.force();
    }

    func f1() {
        var a;
        // a is uninitialized so it has a default null value
        return a;
    }