<?php
declare(strict_types=1);

function test() {
    return;
}

// undef warning
echo $test[0];

// undef warning
echo $test['test'];


//copy by reference empty variable
$copy = &$test;

// no warnings, ref is NULL
echo $copy[0];
echo $copy['test'];

// NULL printed
echo var_dump($copy[0]);


?>