"Object Required" error in IE from $.map over array of dom elements

For

$.m开发者_如何学JAVAap(holder[i], function (elem, index) {

    if (elem.nodeType === 1) {
        var attr = "";
        if (typeof elem.attributes !== 'undefined') {
            attr = ' ' + elem.attributes[0].name + '=' + '"' + elem.attributes[0].nodeValue + '"';
        }
        return '<' + elem.nodeName + attr + '>' + elem.textContent + '</' + elem.nodeName + '>';
    } else if (elem.nodeType === 3) {
        return elem.textContent
    }
});

Where holder[i] is an array of nodes gotten from iterating over XML with

$('[btn-label="' + title + '"] flashtext', myXML).each(function(){ holder.push($(this).contents().get()); });

why could I be getting the error "Object Required" in IE7? Says the problem is here:

if (typeof elem.attributes !== 'undefined' )

This is because the attributes property of a jQuery object will never be undefined, but will be null (e.g. a text node), an empty array (for a tag with no attributes, e.g. <strong>) or a array of associative arrays.