<?php

$test = NULL;

$a = NULL;
$b = false;
$c = 0;
$d = 'aaa';

foreach (array($a, $b, $c, $d) as $item) {
    echo var_export($item, true) . ' ' . ($item != NULL ? 'does' : 'does NOT') . ' match the condition' . PHP_EOL;
}