docs: def add_asset(self, asset_id, asset_content_id=None, label=None, asset_content_type=None):
          """stub"""
          if asset_id is None:
              raise NullArgument('asset_id cannot be None')
          if not isinstance(asset_id, Id):
              raise InvalidArgument('asset_id must be an Id instance')
          if asset_content_id is not None and not isinstance(asset_content_id, Id):
              raise InvalidArgument('asset_content_id must be an Id instance')
          if asset_content_type is not None and not isinstance(asset_content_type, Type):
              raise InvalidArgument('asset_content_type must be a Type instance')
          if label is None:
              label = self._label_metadata['default_string_values'][0]
          else:
              if not self.my_osid_object_form._is_valid_string(
                      label, self.get_label_metadata()) or '.' in label:
                  raise InvalidArgument('label')
          if asset_content_type is None:
              asset_content_type = ''
  
          self.my_osid_object_form._my_map['fileIds'][label] = {
              'assetId': str(asset_id),
              'assetContentTypeId': str(asset_content_type)
          }
  
          if asset_content_id is not None:
              self.my_osid_object_form._my_map['fileIds'][label].update({
                  'assetContentId': str(asset_content_id)
              })