If the file doesn't exist this function won't be called (https://github.com/puppetlabs/cfacter/pull/33/files#diff-4e8a30a08a9e2a1fd33c5bfced7aaf60R21), and I would rather avoid returning empty strings as facts if a given fact is not defined. Do you think we should go the other way and always return something to indicate that a fact was defined but could not be resolved?