Right now if you have two intervals `a` and `b` and one of them is empty, the operations `a + b` and `a - b` throw an `ArgumentOutOfRangeException.`. Making these operations simply return an empty interval instead would simplify calling code and actually fits the semantics of intervals well ("The sum of `a` and `b` is the interval of all values `x + y` for `x` from `a` and `y` from `b`"). I therefor suggest we make these operation return empty intervals in said case. I already tried to check if the exceptions are handled anywhere, which does not seem to be the case. Any reason not to do it?