- var_dump: documentation ( source)
<?php
$a = array(
'one' => 1,
'two' => 2,
'three' => '0',
'four' => null,
'five' => ''
);
var_dump(isset($a['three']));
var_dump(empty($a['three']));
var_dump(isset($a['four']));
var_dump(empty($a['four']));
var_dump(isset($a['five']));
var_dump(empty($a['five']));