JuniorTheoryCommon

What happens when you run this program?

PHP

<?php

$colors = ['red', 'green'];
echo $colors[1], "\n";
echo $colors[2] ?? 'none', "\n";
echo $colors[2], "\n";

green, none, then a Warning: Undefined array key 2

Expecting a missing key to read as a silent null: PHP prints Warning: Undefined array key 2 first, then reads null, so echo prints an empty line.
Expecting the script to stop at $colors[2]: a missing key is a warning, not a fatal error, so that line still prints and the script runs on.

JuniorTheoryCommon

PHP

<?php

$colors = ['red', 'green'];
echo $colors[1], "\n";
echo $colors[2] ?? 'none', "\n";
echo $colors[2], "\n";

green, none, then a Warning: Undefined array key 2

Expecting a missing key to read as a silent null: PHP prints Warning: Undefined array key 2 first, then reads null, so echo prints an empty line.
Expecting the script to stop at $colors[2]: a missing key is a warning, not a fatal error, so that line still prints and the script runs on.