iPhone FaceBook Connect returns NULL email if not shared

I have integrated facebook connect into my Xcode 4 project for an iPhone. Here is the code for iPhone FBconnec. FBconnect.h and 开发者_StackOverflow社区FBSession.h already included.

- (void)viewDidLoad{ _session = [[FBSession sessionForApplication:@"APPKey" 
                                      secret:@"APPSecret" 
                                    delegate:self]retain];

FBLoginButton* fbButton = [[[FBLoginButton alloc] init] autorelease];
fbButton.frame = CGRectMake(228, 50, 85, 50);
[self.view addSubview:fbButton]; }

The code is working fine, but for some facebook accounts when run the FQL query to select email from user. I get NULL as shown below

length of users Array: (
    {
    "contact_email" = "<null>";
    email = "<null>";
    "first_name" = Ali;
    "last_name" = Subhani;
    uid = 696377693;
}

How can I get the extended permission. I am just using following code to run the query. Which contains word params, I think it has to do something with FBRequest. Have a look at the code below

- (void)getFacebookName {

//==================== MAKING FACEBOOK REQUEST =============================
NSString* fql = [NSString stringWithFormat:
                 @"select uid,first_name,last_name,email from user where uid == %lld",
                 self._session.uid];
NSDictionary* params =
[NSDictionary dictionaryWithObject:fql
                            forKey:@"query"];

[[FBRequest requestWithDelegate:self]
 call:@"facebook.fql.query" params:params];}

Where should I enter extended permissions so I can get user email.

Thanks.

I use

[appDelegate.facebook authorize:
  [NSArray arrayWithObjects:
    @"offline_access", @"email", @"user_checkins", @"publish_checkins", nil]
                       delegate:delegate 
                     localAppId:localAppId];

...to authorize and request email access (using the @"email" permissions key above). I'm not sure if a user can have NO email address, as they have at least one to login with.

However, Facebook gives the user the option to obfuscate it from you with an arbitrary @facebook.com account that forwards to their regular email account.