Adds support for Floating IP

If there are other cases where *write* operations return `null` on a 404, I'd say to change them all, or open issues to track them. What does a `null` return value mean on an update (or in general a *write* operation? There are many possible meanings and interpretations and the client doesn't have a way to know which one is true:

* The resource has been updated to `null`?
* The operation did not complete?
* The operation completed but there was no response (typical 204 No-Content)? 
* The operation failed with a 404 because the resource did not exist?

I'd suggest to get rid of this practice and fail. If this is an extended practice, then I'd say to open an issue and identify and change the other cases. AFAIK this practice is not used in a majority of providers.