Cannot iterate over iterator with array_walk since php 7.4

$iterator = new ArrayIterator([1, 2]);
array_walk($iterator, function($item) {echo $item . PHP_EOL;});

This piece of php code outputs the items (1 and 2) in php 7.3 but it outputs nothing in php 7.4. Can anyone explain what changed in php 7.4 that resulted in this change ? I cannot find anything related to that in the changelogs.