Based on my question, i want to set Contract Type : File to null or allow if people doesn't attach a file.
i got the answer, just change operations from "script" to "Contract Input" and it works, thanks antoine to help me and giving me an example.
Thank you so much .
The "file upload and download example" demonstrate how to have optional document upload.
Thank you for your kindness to reply and giving me an example, but when i executed both of upload or don't upload i got this error.