FAISS load to None
CONTRIBUTOR
Hello,

I'm not sure I understand. 
The return value of `ds.load_faiss_index` is None as expected.

I see that loading an Index on a dataset that doesn't have an `embedding` column doesn't raise an Issue. Is that the issue?

So `ds` doesn't have an `embedding` column, but we load an index that looks for it. But this will raise an issue only when calling `ds.search`.
2024-05-16T20:43:56Z
https://github.com/huggingface/datasets/issues/6887#issuecomment-2116144278
https://api.github.com/repos/huggingface/datasets/issues/6887
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https://api.github.com/repos/huggingface/datasets/issues/comments/2116144278/reactions
2024-05-16T20:44:23Z
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### Describe the bug

I've use FAISS with Datasets and save to FAISS.

Then load to save FAISS then no error, then ds to None

```python
ds.load_faiss_index('embeddings', 'my_index.faiss')
```

### Steps to reproduce the bug

# 1.
```python
ds_with_embeddings = ds.map(lambda example: {'embeddings': model(transforms(example['image']).unsqueeze(0)).squeeze()}, batch_size=64)

ds_with_embeddings.add_faiss_index(column='embeddings')

ds_with_embeddings.save_faiss_index('embeddings', 'index.faiss')
```

# 2.
```python
ds.load_faiss_index('embeddings', 'my_index.faiss')
```

### Expected behavior

Add column in Datasets.

### Environment info

Google Colab, SageMaker Notebook