Description:
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Unsetting a non-existing key on an ArrayObject triggers a notice (even a warning in PHP 8),
while it doesn't on an array.

More complete example: https://3v4l.org/WVJnf

Test script:
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<?php

$arr = array();
unset($arr['nonexisting_1']);

$obj = new ArrayObject();
unset($obj['nonexisting_2']);

Expected result:
----------------
(nothing)

Actual result:
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Notice: Undefined index: nonexisting_2 in [...] on line 7