jQuery 1.7 and .attr()

There's a problem here in jQuery 1.7:
var clone = $('')
.attr('href', $(breadcrumb[key]).attr('href'))
.attr('class', $(breadcrumb[key]).attr('class'))
.html($(breadcrumb[key]).html())

If $(breadcrumb[key]).attr('class') is undefined, .attr will return a string and .html will fail.