array_diff() error when passing multidimensional arrays

array-diff-with-multidimensional-arrays-error.php

<?php

$a = [
    'a' => [
        'b' => 'Hello',
    ],
];

$b = [
    'a' => [
        'b' => 'Goodbye',
    ],
];

$result = array_diff($a, $b);

var_dump($result);

/*
PHP 7.4 error:

PHP Notice:  Array to string conversion in file.php on line...
array(0) {
}


PHP 8.0 error:

PHP Warning: Array to string conversion in file.php on line...
array(0) {
}
*/