def preprocess(self, payload: FileData | None) -> str | None:
        """
        Parameters:
            payload: the uploaded file as an instance of `FileData`.
        Returns:
            Passes the uploaded file as a {str} filepath to the function.
        """
        if payload is None:
            return payload
        return payload.path

        Parameters:
            payload: the uploaded file as an instance of `FileData`.
        Returns:
            Passes the uploaded file as a {str} filepath to the function.
        
gradio/components/model3d.py