[jQuery] unfefined properties (filtering jquery by class)

[jon]

My goal is to pull out all anchor tags and replace the href value with
a rewritten value (based on original href).  However, i am getting
errors indicating that the object or property is undefined when there
are no anchor tags with the given class name (which is why i used
filter...)

I have the following href pattern:

File Library/filename

i need it to be

/newPath?library=File+Library&component=filename

This works as long as at least one anchor tag exists of the
appropriate style class but not when only standard anchor tags are
present.

example:
        function rewriteFileHref() {

                library = 
$("a").filter(".changeHrefToWcm").attr("href").split("/")
[0].replace(" ", "+");
                id =$("a").filter(".changeHrefToWcm").attr('href').split("/") 
[1];

                $("a").filter(".changeHrefToWcm").attr('href','/NewLocation/
WcmRenderServlet/?library='+library+'&component='+id);
        }