Description:
------------
No hidden state should be used for next index.

In example below, empty array is set and cleared immediatelly. When array is clear, next index should be 0 like when the 2nd (set/clear) line would not be presented.

Test script:
---------------
$a = [];

$a[] = 'x'; unset($a[0]); // this should have zero effect

$a[] = 5; // but it has, this value is added under index 1 instead of 0

print_r($a);

Expected result:
----------------
Array
(
    [0] => 5
)


Actual result:
--------------
Array
(
    [1] => 5
)