How to differentiate not set parameter from $false, 0, empty string?

I have function that updates object in WMI. I want user to be able to specify in parameters only values that he wants to update. How can I do it?

function UpdateObject ([bool] $b1, [bool] $b2, [int] $n1, [string] $s1)
{
    $myObject = GetObjectFromWmi #(...)
    #(...)

    #This is bad. As it overrides all the properties.
    $myObject.b1 = $b1
    $myObject.b2 = $b2
    $myObject.n1 = $n1
    $myObject.s1 = $s1

    #This is what I was thinking but don't kwow how to do
    if(IsSet($b1)) { $myObject.b1 = $b1 }
    if(IsSet($b2)) { $myObject.b2 = $b2 }
    if(IsSet($n1)) { $myObject.n1 = $n1 }
    if(IsSet($s1)) { $myObject.s1 = $s1 }

    #(...) Store myObject in WMI.
}

I tried passing $null as as parameter but it get's automaticly converted to $false for bool, 0 for int and empty string for string

What are your suggestions?