modProcessorResponse::isError() returns true on getlist processors in PHP 5.4

$response = $modx->runProcessor('resource/getlist');

var_dump($response->isError());

public function isError() {
    return empty($this->response) || empty($this->response['success']);
}

$response = $modx->runProcessor('resource/getlist');

var_dump(empty($response->response)); // false on 5.4 and 5.3
var_dump(empty($response->response['success'])); // false on 5.3 and true on 5.4 + Warning Illegal string offset 'success' 

$response = $modx->runProcessor('resource/getlist');
if ($response instanceof modProcessorResponse) {
  if ($response->isError()) {
    echo 'Something went wrong: ' . $response->getMessage();
  } else {
    echo 'All good!';
  }
} else {
  echo 'This shouldn\'t happen';
}

$response = $this->runProcessor('web/thread/get', $data);
if ($response->isError()) {
	return $response->getMessage();
}
$data = json_decode($response->response,true);

return (!isset($this->response)) || empty($this->response) || (!isset($this->response['success'])) || empty($this->response['success']);

if (!isset($response->response)) {
    $error = $response->getMessage();
    return $error;
}
$responseArray = $response->getResponse();
return $responseArray;