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[YuWei-CH]

1. Add a check_files_not_empty() in job.py to ensure that user uploaded file is not empty
2. I would like to suggest that, regardless of whether we succeed or not, we should keep the upload folder. While reform.py can run successfully, there is a very small chance that the user might still get an incorrect result due to potential bugs in reform.py. If you believe this possibility can be safely ignored, I will update the code to remove the upload folder when the process completes successfully.