define the method __init__ with 15 elements: self, title, link, description, language set to None, author_email set to None,
def __init__ ( self , title , link , description , language = None , author_email = None , author_name = None , author_link = None , subtitle = None , categories = None , feed_url = None , feed_copyright = None , feed_guid = None , ttl = None , ** kwargs ) :