I want to parse the XML body and want to capture the url from the xml body in the list of string which i have created but i am getting Null values in the list

Respnse body:-

```
 <retours>
  <flux>
    <id>WSfv3vWBFA55L6RMQ28FOh9</id>
    <retour>
      <publication>20181026114057</publication>
      <production>20181026114057</production>
      <nature>10</nature>
      <statut>OK</statut>
      <id>AE.yxLo5IC</id>
      <url>https://telecharge.com</url>
    </retour>
    <retour>
      <publication>20181026114058</publication>
      <production>20181026114058</production>
      <nature>11</nature>
      <statut>KO</statut>
      <id>APAyxLo6K1</id>
      <url>https://telecharge1.com</url>
    </retour>
  </flux>
</retours>

```

Below Code in Apex for the parsing:

```
HttpResponse response1 = http.send(request1);
if (response1.getStatusCode() == 200) {
    //system.debug('Body ---->'+response1.getbody());  
    DOM.Document doc = response1.getBodyDocument();
    //DOM.XmlNode rootNode = doc.getRootElement();
    //parseXML(rootNode);
    list<string> urls=new list<string>();

    for (Dom.XmlNode node : doc.getRootElement().getChildElements()) {
        String url = node.getAttributeValue('url', '');
        //Integer score = Integer.valueOf(node.getAttributeValue('_CreditScore', ''));
        urls.add(url);
    }

    system.debug('urls.size--->'+urls.size());

}
else{
    System.debug('The status code returned was not expected: ' +
                 response1.getStatusCode() + ' ' + response1.getStatus());
    System.debug(response1.getBody());
}

```