Well, my thinking is that the slugifier should be as simple as possible - it should just be a filter that does not worry about implementation details, I think if the implementing class decides to return a non-empty string when given an empty string that is its decision.

I have created a wiki page on `symfony-cmf` which lists all the slugifiers I have found and have listed some of the features of each.

 * 3/4 slugifiers specify a separator in the signature, e.g. `function slugify($string, $separator = '-')`
 * 3/4 slugifiers return an empty string if given an empty string.
 * None of the slugifiers throw exceptions.