out.txt

elliotttf@4kmba:~$ php /tmp/test.php

Notice: Undefined index: baz in /private/tmp/test.php on line 15

Notice: Undefined index: baz in /private/tmp/test.php on line 16

test.php

<?php

error_reporting(E_ALL);
$a = array(
  'foo' => array(
    'bar' => array()
  )
);

if (isset($a['foo']['bar']['baz']['bang']['boom'])) {
  print_r($a['foo']['bar']['baz']);
}

// Intentionally raise some notices so we know it's working...
print_r($a['foo']['bar']['baz']);
print_r($a['foo']['bar']['baz']['bang']);
echo PHP_EOL;