def add_hex_strings(input1: str, input2: str = "0") -> str:
    """Return sum of two hex strings.

    Args:
        input1 (str): Hex formatted string.
        input2 (str, optional): Hex formatted string. Defaults to "0".

    Returns:
        str: Hex string sum.
    """
    if input1 is None:
        return ""
    return hex(int(input1, 16) + int(input2, 16))