I'm assuming we're doing this because Facter::Util::Resolution.exec can return a string or nil. However, it's handling validation that the caller should be handling. It would be better in this method just to assume that the input value is a string.

The reason we want to do this is because as this method is currently implemented will cause an incorrect value to fail quietly, when if we're receiving the wrong kind of input it would be better to fail fast.