docs: def set_journal_comment(self, comment=None):
          """Sets a comment.
  
          arg:    comment (string): the new comment
          raise:  InvalidArgument - comment is invalid
          raise:  NoAccess - metadata.is_readonly() is true
          raise:  NullArgument - comment is null
          compliance: mandatory - This method must be implemented.
  
          """
          if comment is None:
              raise NullArgument()
          metadata = Metadata(**settings.METADATA['comment'])
          if metadata.is_read_only():
              raise NoAccess()
          if self._is_valid_input(comment, metadata, array=False):
              self._my_map['journalComment']['text'] = comment
          else:
              raise InvalidArgument()