Detecting param variable input only

I have a script with a standard string param in it. In the script, I want to detect if this string is $null. I've included a script snippet. Rather than using 2 variables, is it possible to set a condition only on the parameter? Something like setting a type of [param] like if ([param]$x) ?

param($x)
 
$somearray = 'product1′,'product2′
 
foreach ($element in $somearray) {
    ## I only want to test against the $x set by the param
    ## I don't want this if $x was set lower in the script
    if (!$x) {
       do something
    }
    ……
    …….
    $x = 'something'
}