anchor.diff:      Account account = createAccount(form, formBinding);
       if (account != null) {
           SignInUtils.signin(account.getUsername());
  -        ProviderSignInUtils.handlePostSignUp(account.getUsername(), request);
  +        ProviderSignInUtils.doPostSignUp(account.getUsername(), request);
           return "redirect:/";
       }
       return null;
  
positive.code: Before redirecting to the sign up page, `ProviderSignInController` collects some information about the authentication attempt. 
  This information can be used to prepopulate the sign up form and then, after successful sign up, to establish a connection between the new account and the provider account.
  
  To prepopulate the sign up form, you can fetch the user profile data from a connection retrieved from `ProviderSignInUtils.getConnection()`.
  For example, consider this Spring MVC controller method that setups up the sign up form with a `SignupForm` to bind to the sign up form:
  
  ```java
  @RequestMapping(value="/signup", method=RequestMethod.GET)
  public SignupForm signupForm(WebRequest request) {
      Connection<?> connection = ProviderSignInUtils.getConnection(request);
      if (connection != null) {
          return SignupForm.fromProviderUser(connection.fetchUserProfile());
      } else {
  
negative.code: Twitter, for example, does not provide a user's email address, so the `getEmail()` method will always return null after a sign in attempt with Twitter.
  
  After the user has successfully signed up in your application a connection can be created between the new local user account and their provider account. 
  To complete the connection call `ProviderSignInUtils#doPostSignUp()`. 
  For example, the following method handles the sign up form submission, creates an account and then calls `ProviderSignInUtils#doPostSignUp()` to complete the connection:
  
  ```java
  @RequestMapping(value="/signup", method=RequestMethod.POST)
  