Why there is no data send to data_collator?
### System Info

- `transformers` version: 4.27.0.dev0
- Platform: Linux-3.10.0-514.el7.x86_64-x86_64-with-centos-7.3.1611-Core
- Python version: 3.7.13
- Huggingface_hub version: 0.12.0
- PyTorch version (GPU?): 1.13.1+cu117 (True)
- 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?

@sgugger 

### Information

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

### Tasks

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

### Reproduction

**I'm tring to us code below**


And get error `KeyError: 'seq2seq'`, after output feature input to data_collator, get output like follow:
`[{}, {}, {}, {}]`
Why this happened? I output train dataset and get correct result, but when using `trainer.train()` it can get data I need.
[train.txt](https://github.com/huggingface/transformers/files/11035839/train.txt)


### Expected behavior

How can I send data in training process? Thanks for your help.
That's related to the data you are preprocessing, not the Transformers library or its examples. There is simply no `"seq2seq2"` in the features you prepare with your function. I suggest posting on the [forums](https://discuss.huggingface.co/) to get help from the larger community.<|||||>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.