def human_size(num_bytes: int | None) -> str:
    if not num_bytes:
        return ""

    units = ["B", "KB", "MB", "GB", "TB", "PB"]
    size = float(num_bytes)

    for unit in units:
        if size < 1024 or unit == units[-1]:
            s = f"{size:.3f}".rstrip("0").rstrip(".")
            if "." not in s:
                s += ".0"
            return f"{s} {unit}"
        size /= 1024