The resolution of facts will be used in puppet, and returning the string "unknown" will make it more difficult to write conditional statements using this fact. For example:

```puppet
# in the puppet dsl
if $operatingsystemrelease {
  # do things
}
# vs
if $operatingsystemrelease == 'unknown' {
  # do stuff
}
```
Currently the behavior for BlueWhite and Slamd is to return the string "unknown", but since this pull request is targeted at master it's okay to make a breaking change and remove this undesirable behavior.

In other words, what you want to do here is: 

```ruby
if match = other_stuff[:regexp].match(release)
  match[1]
end
```

and just leave out the else entirely so that we won't return anything if there isn't a match.