Evaluating an Expression in PHP That Has ==0 Inside

Question

I have code like this:

$thi = $dinfoarray->totalItems;
        var_dump($thi);
        // $thi is NULL
    if ($thi == 0) {
       // execute code here if $thi = 0.
    else {
        print "We have issues. The query is: $queryl";
        die();
    }

the if part is meant to execute when $thi is integer 0. But when var_dump shows that $thi = NULL, the if part still executes. Why, and how do I make it work?