如果字段为空，如何跳过RSS项？

Another little thing has been driving me crazy... I want to pull in an RSS feed and display it using PHP. It asks for the mrss decription (because it doesn't have all the extra junk attached to it). The only problem is that the feed has advertisements. So when the script calls for the media description of an advertisement (for which there is none), the whole page fails. Another little thing has been driving me crazy.