OpenSAML user discussion

Hello World!,
      I am using opensaml2 java ,when trying to execute sample code given in 
user manual of opensaml i am getting following error.




public class HelloworldSAML {

        public static void main( String[] args) {         

            try {
                // Get the builder factory
            XMLObjectBuilderFactory builderFactory = 
Configuration.getBuilderFactory();

  // Get the assertion builder based on the assertion element name
            AssertionBuilder builder = (AssertionBuilder) 
builderFactory.getBuilder(Assertion.DEFAULT_ELEMENT_NAME);

  // Create the assertion
            Assertion assertion = builder.buildObject();


            } catch (Exception e) {
                e.printStackTrace();
        }

}

Error:
  java.lang.NullPointerException
        at Helloworld.main(Helloworld.java:35)


I am using opensaml from this link
http://shibboleth.internet2.edu/downloads/opensaml2/java/tp1/

please help me.

thanks
harsha