[facebook/rag-sequence-nq] ValueError: Config name is missing. 
Author: zhangnju
Pull request: no

### System Info

- `transformers` version: 4.36.2
- Platform: Linux-5.15.0-91-generic-x86_64-with-glibc2.29
- Python version: 3.8.10
- Huggingface_hub version: 0.20.1
- Safetensors version: 0.4.1
- Accelerate version: 0.25.0
- Accelerate config:    not found
- PyTorch version (GPU?): 1.13.1+cpu (False)
- Tensorflow version (GPU?): not installed (NA)
- Flax version (CPU?/GPU?/TPU?): not installed (NA)
- Jax version: not installed
- JaxLib version: not installed
- Using GPU in script?: <fill in>
- Using distributed or parallel set-up in script?: <fill in>

### Who can help?

_No response_

### Information

- [X] The official example scripts
- [ ] My own modified scripts

### Tasks

- [X] An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)
- [ ] My own task or dataset (give details below)

### Reproduction

1.run the sample codes of this link: https://huggingface.co/facebook/rag-sequence-nq 
from transformers import RagTokenizer, RagRetriever, RagSequenceForGeneration 
 
tokenizer = RagTokenizer.from_pretrained("facebook/rag-sequence-nq") 
retriever = RagRetriever.from_pretrained("facebook/rag-sequence-nq", index_name="exact", use_dummy_dataset=True) 
model = RagSequenceForGeneration.from_pretrained("facebook/rag-sequence-nq", retriever=retriever) 
 
input_dict = tokenizer.prepare_seq2seq_batch("how many countries are in europe", return_tensors="pt") 

generated = model.generate(input_ids=input_dict["input_ids"]) 
print(tokenizer.batch_decode(generated, skip_special_tokens=True)[0]) 

2. meet the below issue 
Traceback (most recent call last):
  File "rag_test.py", line 4, in <module>
    retriever = RagRetriever.from_pretrained("facebook/rag-sequence-nq", index_name="exact", use_dummy_dataset=True)
  File "/usr/local/lib/python3.8/dist-packages/transformers/models/rag/retrieval_rag.py", line 443, in from_pretrained
    index = cls._build_index(config)
  File "/usr/local/lib/python3.8/dist-packages/transformers/models/rag/retrieval_rag.py", line 423, in _build_index
    return CanonicalHFIndex(
  File "/usr/local/lib/python3.8/dist-packages/transformers/models/rag/retrieval_rag.py", line 278, in __init__
    dataset = load_dataset(
  File "/usr/local/lib/python3.8/dist-packages/datasets/load.py", line 2519, in load_dataset
    builder_instance = load_dataset_builder(
  File "/usr/local/lib/python3.8/dist-packages/datasets/load.py", line 2228, in load_dataset_builder
    builder_instance: DatasetBuilder = builder_cls(
  File "/usr/local/lib/python3.8/dist-packages/datasets/builder.py", line 371, in __init__
    self.config, self.config_id = self._create_builder_config(
  File "/usr/local/lib/python3.8/dist-packages/datasets/builder.py", line 576, in _create_builder_config
    raise ValueError(
ValueError: Config name is missing.
Please pick one among the available configs: ['psgs_w100.nq.exact', 'psgs_w100.nq.compressed', 'psgs_w100.nq.no_index', 'psgs_w100.multiset.exact', 'psgs_w100.multiset.compressed', 'psgs_w100.multiset.no_index', 'psgs_w100.nq.exact.no_embeddings', 'psgs_w100.nq.compressed.no_embeddings', 'psgs_w100.nq.no_index.no_embeddings', 'psgs_w100.multiset.exact.no_embeddings', 'psgs_w100.multiset.compressed.no_embeddings', 'psgs_w100.multiset.no_index.no_embeddings']
Example of usage:
        `load_dataset('wiki_dpr', 'psgs_w100.nq.exact')`

### Expected behavior

help the sample codes to run successfully 

Comments:
Maybe cc @ydshieh as you have played with RAG recently. 

Hi @zhangnju 

What is your `datasets` version?

On [this google colab](https://colab.research.google.com/drive/1pCLInwexxrwg2WGIxgjmFMs6YeHZsCOm?usp=sharing), I can't reproduce this issue, but it uses `datasets==2.16.1`.

This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.