def preprocess(
        self, payload: ListFiles | FileData | None
    ) -> bytes | str | list[bytes] | list[str] | None:
        """
        Parameters:
            payload: File information as a FileData object, or a list of FileData objects.
        Returns:
            Passes the file as a `str` or `bytes` object, or a list of `str` or list of `bytes` objects, depending on `type` and `file_count`.
        """
        if payload is None:
            return None
        if self.file_count == "single":
            if isinstance(payload, ListFiles):
                return self._process_single_file(payload[0])
            return self._process_single_file(payload)

        if isinstance(payload, ListFiles):
            return [self._process_single_file(f) for f in payload]  # type: ignore
        return [self._process_single_file(payload)]  # type: ignore

        Parameters:
            payload: File information as a FileData object, or a list of FileData objects.
        Returns:
            Passes the file as a `str` or `bytes` object, or a list of `str` or list of `bytes` objects, depending on `type` and `file_count`.
        
gradio/components/upload_button.py