setWadlUrl returns null

Hi, Im trying to generate REST requests from a WADL.

I am using this code:

project = new WsdlProject();
   config = RestServiceConfig.Factory.newInstance();
   config.setDefinitionUrl(url);
   service = new RestService(project, config);
   service.setWadlUrl(url);
   System.out.println("URL: " + service.generateWadlUrl());

in this case, the url is the location of the wadl.
when I run this function, the output is:

URL: null.wadl

any idea why its not retrieving the wadl?