code: def _index_command(self, type, columns, index):
          
          if not isinstance(columns, list):
              columns = [columns]
  
          if not index:
              index = self._create_index_name(type, columns)
  
          return self._add_command(type, index=index, columns=columns)
docs: Add a new index command to the blueprint.
  
          :param type: The index type
          :type type: str
  
          :param columns: The index columns
          :type columns: list or str
  
          :param index: The index name
          :type index: str
  
          :rtype: Fluent