Ajax XML response, errors when empty

Basically, it links to a PHP file which gets information from a database and formats it as XML. The problem is, I get javascript errors when I try to assign a tag value to a string when the xml tag is empty.

The error happens about here

[CODE]var title = xmlDocument.getElementsByTagName(“title”)[0].firstChild.data;
var description = xmlDocument.getElementsByTagName(“keywords”)[0].firstChild.data;
var keywords = xmlDocument.getElementsByTagName(“description”)[0].firstChild.data;
var content = xmlDocument.getElementsByTagName(“content”)[0].firstChild.data;[/CODE]

I think the error is something along the lines of ‘Object expected’;

heres the code…

[CODE]<script language=”javascript”>
var XMLHttpRequestObject = false;

if (window.XMLHttpRequest) {
XMLHttpRequestObject = new XMLHttpRequest();
} else if (window.ActiveXObject) {
XMLHttpRequestObject = new ActiveXObject(“Microsoft.XMLHTTP”);
}

function getData(dataSource, divID) {
if(XMLHttpRequestObject) {
var obj = document.getElementById(divID);
XMLHttpRequestObject.open(“POST”, dataSource);
XMLHttpRequestObject.setRequestHeader(“Content-Type”,”application/x-www-form-urlencoded”);
XMLHttpRequestObject.onreadystatechange = function() {
if (XMLHttpRequestObject.readyState == 4 &&
XMLHttpRequestObject.status == 200) {
xmlDocument = XMLHttpRequestObject.responseXML;
var title = xmlDocument.getElementsByTagName(“title”)[0].firstChild.data;
var description = xmlDocument.getElementsByTagName(“keywords”)[0].firstChild.data;
var keywords = xmlDocument.getElementsByTagName(“description”)[0].firstChild.data;
var content = xmlDocument.getElementsByTagName(“content”)[0].firstChild.data;
document.write(title);
document.write(description);
document.write(keywords);
document.write(content);
}
}
XMLHttpRequestObject.send(“id=25”);
}
}
</script>[/CODE]

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