weburilookup method: stable way to flag that destination does not exist?

Alameth

I'd like to provide an option in my uploader to API 2.0 to automatically create the destination album (a.k.a. gallery) if it does not already exist. Currently I am using the weburilookup method to find the destination album. It works well if the album exists and is an album, and it's clear enough when the URI is a folder, page, or albumimage. But the response is strange when the URI doesn't exist or is nonsense.

What is the correct way to interpret the weburilookup response to mean "does not exist"? Check the locator? Infer it from the absense of a Page, Album, or Folder in the response? (I hate inferring an error response from the lack of a known response; what happens if you add a new type?)