I'm just a beginner trying to learn some AJAX so my question may be dumb. When I open this document in my browser, I click the button on the page and get the error "Uncaught TypeError: Cannot set property 'innerHTML' of null". I've tried to fix this, and even removed the line with the innerHTML property and the same error involving innerHTML keeps showing up, how's that even possible? would appreciate some help.

```
    <!doctype html>
<html>
<head>
    <script type="text/javascript">

    function cargaXML(){

        var conexion;
        var txt,x,i;

        if(window.XMLHttpRequest){
                        conexion = new XMLHttpRequest();
                    } else {
                        conexion = new ActiveXObject("Microsoft.XMLHTTP");
                    }

        conexion.onreadystatechange = function(){
            if (conexion.readyState == 4 && conexion.status == 200){
                xmlDoc = conexion.responseXML;
                txt = "<table>";
                x = xmlDoc.getElementsByTagName("titulo");
                artista = xmlDoc.getElementsByTagName("artista");
                pais = xmlDoc.getElementsByTagName("pais");
                firma = xmlDoc.getElementsByTagName("firma");
                precio = xmlDoc.getElementsByTagName("precio");
                anio = xmlDoc.getElementsByTagName("anio");

                for (i=0;i<x.length;i++){
                    txt = txt + "<tr><td>" + x[i].childNodes[0].nodeValue + "</td><tr>" + artista[i].childNodes[0].nodevalue + "</td><td>" + pais[i].childNodes[0].nodevalue + "</td><td>" + firma[i].childNodes[0].nodevalue + "</td><td>" + precio[i].childNodes[0].nodevalue + "</td><td>" + anio[i].childNodes[0].nodevalue + "</td>";
                }
                txt = txt + "</table>";
                document.getElementById("myDiv").innerHTML = txt;
            }

            conexion.open("GET","discos.xml",true);
            conexion.send();
        }

        }

    </script>
</head>
<body>
    <h2>Mi colección</h2>
    <div id="myDiv">

    </div>

    <button type="button" onclick="cargaXML()">Tomar mi colección</button>
</body>
</html>

```