You still have to case on the empty list (e.g., you can't get the first value from it, so if you need it, you need to do /something/ different for the empty list unless you want exceptions about incomplete pattern matchings). An example:
safeHead :: [a] -> Maybe a
safeHead  = Nothing
safeHead (a:_) = Just a
When calling safeHead, the caller must* check to see if a value was actually returned before using it. This can be done with fromMaybe:
fromMaybe sensibleDefault $ safeHead someList
* The caller can just use fromJust which raises an exception on a Nothing value, but that's the caller's burden at that point.