code: def get_extr_lics_comment(self, extr_lics):
          
          comment_list = list(self.graph.triples(
              (extr_lics, RDFS.comment, None)))
          if len(comment_list) > 1 :
              self.more_than_one_error('extracted license comment')
              return
          elif len(comment_list) == 1:
              return comment_list[0][2]
          else:
              return
docs: Return license comment or None.