code: def set_creation_comment(self, doc, comment):
          
          if not self.creation_comment_set:
              self.creation_comment_set = True
              if validations.validate_creation_comment(comment):
                  doc.creation_info.comment = str_from_text(comment)
                  return True
              else:
                  raise SPDXValueError('CreationInfo::Comment')
          else:
              raise CardinalityError('CreationInfo::Comment')
docs: Sets creation comment, Raises CardinalityError if
          comment already set.
          Raises SPDXValueError if not free form text.