Issue running run_glue.py at test time
Hi,

I'm using [this script](https://github.com/huggingface/transformers/blob/master/examples/pytorch/text-classification/run_glue.py) to train a model on my own dataset.
(transformers  4.15.0, datasets  1.17.0, python3.7)
I'm doing single sentence classification, and my CSV files have 2 cols: label, sentence1
I can run the script with no issue when --do_train --do_eval --do_predict are true.
However, later, when I use the same test set used when training, but this time with only "--do_predict" on one of the checkpoints of the models I previously trained, I get the following error:

> File "/lib/python3.7/site-packages/datasets/arrow_writer.py", line 473, in <listcomp>
    pa_table = pa.Table.from_arrays([pa_table[name] for name in self._schema.names], schema=self._schema)
  File "pyarrow/table.pxi", line 1339, in pyarrow.lib.Table.__getitem__
  File "pyarrow/table.pxi", line 1900, in pyarrow.lib.Table.column
  File "pyarrow/table.pxi", line 1875, in pyarrow.lib.Table._ensure_integer_index
KeyError: 'Field "sentence2" does not exist in table schema'

I would appreciate any tips on how to fix this, thanks!

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