Bug in espnet-ez trainer

[juice500ml]

Describe the bug

• https://github.com/espnet/espnet/blob/master/espnetez/trainer.py#L197-L198
• valid_dump_dir and train_dump_dir can be None. But it enforces type conversion as Path(...).
• Quick fix would be something like train_dump_dir = Path(train_dump_dir) if train_dump_dir is not None else None.

Basic environments:

• Current codebase will have this problem regardless of version.

Task information:

• ESPnet-EZ

To Reproduce

• Feed None to dump_dir, and dataset object to train_dataset.

Error logs

Traceback (most recent call last):
  File "/ocean/projects/cis240125p/vtiwari2/homework/espnet_tutorial_f2024.py", line 82, in <module>
    trainer = ez.Trainer(
  File "/ocean/projects/cis240125p/vtiwari2/espnet/espnetez/trainer.py", line 197, in __init__
    train_dump_dir = Path(train_dump_dir)
  File "/jet/home/vtiwari2/miniconda3/envs/espnet/lib/python3.9/pathlib.py", line 1082, in __new__
    self = cls._from_parts(args, init=False)
  File "/jet/home/vtiwari2/miniconda3/envs/espnet/lib/python3.9/pathlib.py", line 707, in _from_parts
    drv, root, parts = self._parse_args(args)
  File "/jet/home/vtiwari2/miniconda3/envs/espnet/lib/python3.9/pathlib.py", line 691, in _parse_args
    a = os.fspath(a)
TypeError: expected str, bytes or os.PathLike object, not NoneType

[sw005320]

@Masao-Someki, can you check this?

[Masao-Someki]

Thank you, @juice500ml! I think these two lines would fit between lines 224 and 225. I'll create a PR to fix this.