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<?php $a = [null => '000', 1 => '111' ]; var_dump($a[null]); $a[null] = 'null'; //var_dump($a[null]);
Output for 5.5.0 - 5.5.38, 5.6.0 - 5.6.40, 7.0.0 - 7.0.33, 7.1.0 - 7.1.33, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.27, 8.2.0 - 8.2.17, 8.3.0 - 8.3.4
string(3) "000"

preferences:
237.67 ms | 404 KiB | 326 Q