Null value in response.sendRedirect() causes original url to be invoked 20 times

[Jonathan Mast]

A null value in bounce_url is causing the original Request url to be invoked
exactly 20 times, rather than dying with NullPointerException:

    public static synchronized void doSomething(
        HttpServletRequest request,
        HttpServletResponse response,
        JspWriter out) {

        final String foo = request.getParameter("foo");
        String bounce_url = request.getParameter("bounce");

        if (DataUtils.isValidFoo(foo)) {
            Thread myThread = new Thread(new Runnable() {
                public void run() {
                    FooFactory.foomatic(foo);
                }
            }, "fooFread");
            myThread.start();
        }
        try {
            response.sendRedirect(bounce_url);
        } catch (IOException ex) {
            logger.log(ex);
        }
    }

So basically if the "bounce" parameter is not provided then this snippet of
code ends being invoked 20 times.  If "bounce" is provided then everything
works fine.  Is this a bug in Tomcat?

Java 1.6
Tomcat 6.0.18