title: calling genericmodel validateAndSave method won't have the record id autogenerated
body: <p>I have the following code that create/save a user record, the database is the default (H2 in memory) database. </p>
  
  <p>I expect that, after calling validateAndSave (of GenericModel) API on the user instance, the user will have an id autogenerated. </p>
  
  <p>But I am getting a 404 at client side, ie, the code failed on notFoundIfNull in get method.</p>
  
  <p>Is that correct behavior? </p>
  
  <pre><code>public static void add(String body) {
      User user = new Gson().fromJson(body, User.class);
  
      if (User.findBy(user.email) != null) {
          badRequest();
      }
  
      user.validateAndSave();
  
      get(user.id);
  }
  
  public static void get(Long id) {
      User user = User.findBy(id);
  
      notFoundIfNull(user);
  
      render(user);
  }
  </code></pre>