code: def get_publisher(self, undefined=""):
          
          publishers = set([
              remove_hairs_fn(publisher)
              for publisher in self["260b  "] + self["264b"]
          ])
  
          return _undefined_pattern(
              ", ".join(publishers),
              lambda x: x.strip() == "",
              undefined
          )
docs: Args:
              undefined (optional): Argument, which will be returned if the
                        `publisher` record is not found.
  
          Returns:
              str: Name of the publisher ("``Grada``" for example) or \
                   `undefined` if `publisher` is not found.