Will it always evaluate to FALSE?

I sea this code and as far as I know (I suppose I don't know much), this will evaluate to false won't it?

function __construct($dbuser=null, $dbpassword=null, $dbname=null, $dbhost=null,$newLink=false){
            global $config;
            $this->queryNum = 0;
            if ($dbuser)
            {
}

If it is - what's the point of it?

If not - why?