Description:
------------
Reference to undeclared array element, creates element, instead return null pointer.

Test script:
---------------
$array = array('a');
print_r($array);
$a= &$array[4];
print_r($array);

$array2 = array('b');
print_r($array2);
$a= $array2[4];
print_r($array2);

Expected result:
----------------
Array
(
    [0] => a
)
Array
(
    [0] => a
)

Actual result:
--------------
Array
(
    [0] => a
)
Array
(
    [0] => a
    [4] => 
)