code: def _validate_item_loader(self) -> None:
      assert self._config
      if (
          len(self._config["data_format"]) == 1
          and self._config["data_format"][0].startswith(
              "no_header_tensor"
          )
          and not isinstance(self._item_loader, TokensLoader)
      ):
          raise ValueError(
              "Please, use Cache(..., item_loader=TokensLoader(block_size=...))"
          )
  
imports: import json
  import os
  from typing import Any, Dict, List, Optional, Tuple
  from lightning.data.streaming.constants import _INDEX_FILENAME, _TORCH_GREATER_EQUAL_2_1_0
  from lightning.data.streaming.downloader import get_downloader_cls
  from lightning.data.streaming.item_loader import BaseItemLoader, PyTreeLoader, TokensLoader
  from lightning.data.streaming.sampler import ChunkedIndex
  from lightning.data.streaming.serializers import Serializer
label_desc: Use image node_id 15 for calling the ChunksConfig obj's underlying member method code with example usage: obj._validate_item_loader() without return types