Deleting all episodes in a season folder leaves an empty season folder with no noticable way so solve the problem. Simply editing the series and then closing it will remove the empty folder, but this won't be obvious to newbies and is not elegant. Ideally, the delete routine for episodes would check if the season was empy and update.
You are amazing Alessio. This one is not that big of a deal, but important for people looking at the program. I deleted a TVseries by accident trying to get rid of tha empty folder (not to worry - I just re-imported) and I wouldn't want a potential customer to do the same.