String cannot be turned into array by assignment anymore
-$string = '';
+$string = [];
$string[] = 1;Configure your rector.php:
<?php
use Rector\Config\RectorConfig;
use Rector\Php71\Rector\Assign\AssignArrayToStringRector;
return RectorConfig::configure()
->withRules([
AssignArrayToStringRector::class,
]);