Yes there is a default value, but the error message is triggered when someone defines $sStyle = 'somethinginvalid' (something other than short or full). In that case we return error.
It's not that significant, but maybe we could avoid the error and set $sStyle = 'full' at that point.
Anyway this is not a problem, but a suggestion. 
That is not the case for the error message of course.  If it stays, i believe it should be changed.