Call to a member function xpath() on a non-object?

$xpath = '/html/body/div/div/div[5]/div/div/div[2]/div/div[2]/img';
$html = new DOMDocument();
@$html->loadHTMLFile($target_URL);
$xml = simplexml_import_dom($html);
$source_image = $xml->xpath($xpath);
$source_image = $source_image[0]['src'];

$xpath = '/html/body/div/div/div[5]/div/div/div[2]/div/div[2]/img';
$html = new DOMDocument();
@$html->loadHTMLFile($target_URL);
$xml = simplexml_import_dom($html);
if (!$xml) {
    echo 'Error while parsing the document';
    exit;
}
$source_image = $xml->xpath($xpath);
$source_image = $source_image[0]['src'];