Yes, it does for None and strings (e.g. 'green', 'sin' etc. - first part of the if-test) because operations are not meaningful for those. But not for other values where operations are actually meaningful, including ints, lists, tuples and arrays. 

So I think we're good. At least I can do operations here and there's several of them in the unit tests.

But now that you bring my attention to it, we should raise a warning if people actually try doing operations on None and str. Right now it just silently ignores the operation argument for None and str. I'll look into it and include it in next commit.