code: def add_markdown(self, markdown):
          
          if markdown is None:
              raise NullArgument('markdown cannot be None')
          if not self.my_osid_object_form._is_valid_string(
                  markdown, self.get_markdown_metadata()):
              raise InvalidArgument('markdown')
          self.my_osid_object_form._my_map['markdown'] = markdown
docs: stub