Fix NestedDataStructure.data for empty dict
I validated that this fixed the problem, thank you, @albertvillanova!
 still facing the same issue or similar:
from datasets import load_dataset
wtm14_test = load_dataset('wmt14',"de-en",cache_dir='./datasets')

~\.cache\huggingface\modules\datasets_modules\datasets\wmt14\43e717d978d2261502b0194999583acb874ba73b0f4aed0ada2889d1bb00f36e\wmt_utils.py in _split_generators(self, dl_manager)
    758         # Extract manually downloaded files.
    759         manual_files = dl_manager.extract(manual_paths_dict)
--> 760         extraction_map = dict(downloaded_files, **manual_files)
    761 
    762         for language in self.config.language_pair:

TypeError: type object argument after ** must be a mapping, not list Hi @sabania 
We released a patch version that fixes this issue (1.4.1), can you try with the new version please ?
```
pip install --upgrade datasets
``` I re-validated with the hotfix and the problem is no more. It's working. thanks a lot.
Fix #1981