Improve error message Union not allowed (#17769)
Improve error message Union not allowed (#17769)

* Improve error message Union not allowed

* make style

* Update src/transformers/hf_argparser.py

Co-authored-by: Sylvain Gugger <222c4d44cc8ec39802c192ed0aa3f97cdb77ff4e@users.noreply.github.com>

Co-authored-by: Sylvain Gugger <222c4d44cc8ec39802c192ed0aa3f97cdb77ff4e@users.noreply.github.com>
huggingface/transformers,huggingface/transformers,huggingface/transformers,huggingface/transformers