ZhouXiangZhong

> `extra_file_path` in [code1](https://github.com/L-YeZhu/CDCD/blob/667f9c0156e68d6e884a1ad5201ae1928098b02d/synthesis/data/aist_dataset.py#L43) is None. This results in the `__getitem__()` returns NoneType for negative_music in [code2](https://github.com/L-YeZhu/CDCD/blob/667f9c0156e68d6e884a1ad5201ae1928098b02d/synthesis/data/aist_dataset.py#L109). the same issue, i just delete the negative_music in the data dict. but...