Field value from previous request is recycled when field is absent in new request

This was tested against 2.3.1 and HEAD.

Consider this class:

@Path("/test")
public class Test {
  @QueryParam("q") private String q;

  @GET
  public void test() {
    System.err.println(q);
  }
}

Now consider this test case:

$ curl http://localhost:8080/test       # prints "null"
$ curl http://localhost:8080/test?q=foo # prints "foo"
$ curl http://localhost:8080/test       # prints "foo" !

This is a serious bug because it leaks information. It's not specific to @QueryParam, the other annotations have the same problem.

I discovered it in a resource that is used for authentication: after logging in once, I could log in again without providing a username and password!