Is implicitly using null argument as a flag good code style

Question

Which of below is a better coding style, and why? 1)

public string GetValue(string setting, string error)
{
    var val = GetSettingFromSomewhere(setting);
    if (val==null && string.IsNullOrEmpty(error)) throw Exception(error);
    return val;
}

Or 2)

public string GetValue(string setting, bool isRequired, string error)
{
    var val = GetSettingFromSomewhere(setting);
    if (val==null && isRequired) throw Exception(error);
    return val;
}

Answer 1

IsNullOrEmpty function is Light and it's returning a Boolean so I guess for this case in particular it doesn't really matter. What matters is what you think makes your function more readable to the people who might use the function