Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

You aren't accessing an array offset but a string offset. null is casted to String. The string is shorter than the offset (length is 0) so it returns NULL.

Thank you for your response.

> You aren't accessing an array offset but a string offset. null is casted to String. The string is shorter than the offset (length is 0) so it returns NULL.

Well, PHP emits a notice when accessing uninitialized string offset, so this is not the case:

~: php -r 'error_reporting(E_ALL); $a=""; echo $a[12]; '
PHP Notice:  Uninitialized string offset: 12 in Command line code on line 1
PHP Stack trace:
PHP   1. {main}() Command line code:0

Notice: Uninitialized string offset: 12 in Command line code on line 1

Call Stack:
    0.0002     317032   1. {main}() Command line code:0


Anyway, I guess there should be at least warning, because null is neither a string, nor array, and trying to access element of null is obviously an error, and I, as a developer, would prefer to have it logged.

He has an interesting point.
For arrays you get "undefined offset".
For strings, "uninitialized string offset".
For objects, "cannot use object of type foo as array".
For null, numbers, bools, no error, no nothing.

This has been marked as not a bug.
Yet compared to all other Erros and Notices this should also throw at least a notice.

If this had been cast to a string, it would throw a "Notice: Uninitialized string offset:"

<?php
$array = null;
$value = $array['one']['two'];