Make interval arithmetic handle empty intervals gracefully

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?