why I got "org.w3c.dom.DOMException: HIERARCHY_REQUEST_ERR: An attempt was made to insert a node where it is not permitted exception?

Question

I wrote this code but the mentioned exception thrown. what's wrong, please help? this is the code :

 //-*-*-
    FileInputStream input = new FileInputStream("cv.xml");
    XMLStreamReader reader = XMLInputFactory.newInstance().createXMLStreamReader(input);
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

    //-*-*- get new entries from input stream
    System.out.println("<< Sahar CV >>\n -> Modify the first reference\n    ** Modify The Name **");
    System.out.print("    Enter degree : ");
    String degree = "";//in.readLine();
    System.out.print("    Enter first name : ");
    String fName = "";//in.readLine();
    System.out.print("    Enter last name : ");
    String lName = "";//in.readLine();
    System.out.println("    ** Modify The Address ** ");
    System.out.print("    Enter new city : ");
    String newCity = "";//in.readLine();
    System.out.print("    Enter new country : ");
    String newCountry = "";//in.readLine();

    //-*-*- let the reader point at the first "reference" element
    int eventType;
    boolean ref = false, fname = false;
    while (!ref && reader.hasNext()) {
        eventType = reader.next();
        switch (eventType) {
            case XMLEvent.START_ELEMENT:
                if (reader.getLocalName().equalsIgnoreCase("references")) {
                    ref = true;
                    break;
                }
        }
    }
    System.out.println("I am here");
    reader.nextTag();
    //-*-*- start modification
    Document doc = new DOMConverter().buildDocument(reader);

    Element firstRef = (Element)doc.getElementsByTagName("reference").item(0);
    System.out.println("111");
    NodeList name = (NodeList)firstRef.getElementsByTagName("name");
    //-*-*- modify the degree (Dr. , Eng. , Dev. ,etc)
    Attr att = (Attr)name.item(0).getAttributes().item(0);
    ((Node)att).setNodeValue(degree);
    //-*-*- modify first name
    NodeList firstName = (NodeList)firstRef.getElementsByTagName("fname");
    NodeList firstNameChilds = (NodeList)firstName.item(0).getChildNodes();
    ((Node)firstNameChilds.item(0)).setNodeValue(fName);
    //-*-*- modify last name
    NodeList lastName = (NodeList)firstRef.getElementsByTagName("lname");
    NodeList lastNameChilds = (NodeList)lastName.item(0).getChildNodes();
    ((Node)lastNameChilds.item(0)).setNodeValue(lName);
    //-*-*- modify city
    NodeList city = (NodeList)firstRef.getElementsByTagName("city");
    NodeList cityChilds = (NodeList)city.item(0).getChildNodes();
    ((Node)cityChilds.item(0)).setNodeValue(newCity);
    //-*-*- modify country
    NodeList country = (NodeList)firstRef.getElementsByTagName("country");
    NodeList countryChilds = (NodeList)country.item(0).getChildNodes();
    ((Node)countryChilds.item(0)).setNodeValue(newCountry);

    reader.close();
    input.close();
    //-*-*- write DOM document
    FileOutputStream out = new FileOutputStream("cv.xml");
    XMLStreamWriter sw = XMLOutputFactory.newInstance().createXMLStreamWriter(out);

    new DOMConverter().writeDocument(doc, sw);
    sw.close();
    out.close();