Empty chunks on diff

[gemal]

I have a unit test that sometimes fails

Our code is:

$differ = new Differ();
$msg = $differ->diff($oldData, $newData);

if I do:
print_r($parser->parse($msg));

I get:

array (
  0 => 
  SebastianBergmann\Diff\Diff::__set_state(array(
     'from' => 'Original',
     'to' => 'New',
     'chunks' => 
    array (
    ),
  )),
)

which makes no sense. If chunks are empty, if there really a diff? how can it be empty?