Exception isn't thrown when nil inserted in NSDictionary - ios

Question

So I was working on pulling photos from user's Facebook album and for some reason NSDictionary doesn't throw an exception when nil is inserted.
I've tested it on a real device and on iOS simulator (both iOS 7).
Maybe debugger crashes, maybe it's Facebook SDK bug.
Anyway, I'm ready to listen to your opinion.
UPDATE: One more thing I forgot to mention. In debugger, after inserting nil object in dictionary, debugger itself continues program execution. And I'm not even pressing the buttong "Continue program execution".
Here's the snippet
- (void)downloadAlbumsWithCompletionBlock:(void (^)(NSArray *albums, NSError *error))completionBlock;
{
[FBRequestConnection startWithGraphPath:#"/me/albums"
parameters:nil
HTTPMethod:#"GET"
completionHandler:^(FBRequestConnection *connection, id result, NSError *error)
{
if (error)
{
NSLog(#"%#", error.localizedDescription);
completionBlock(nil, error);
}
else
{
NSMutableArray *data = [result objectForKey:#"data"];
NSMutableArray *albums = [NSMutableArray new];
for (NSMutableDictionary *dict in data)
{
NSString *albumID = dict[#"id"];
NSString *coverPhotoID = dict[#"cover_photo"];
// coverPhotoID gets nil and then successfully gets put in NSDictionary
// You can just write "NSString *coverPhotoID = nil;".
NSString *description = dict[#"description"];
NSString *name = dict[#"name"];
NSDictionary *album = #{#"album_id": albumID,
#"album_cover_photo_id": coverPhotoID,
#"album_description": description,
#"album_name": name };
// Here an exception should be thrown but for some reason
// we just quit out of the method. Result would be the same if we put
// empty "return;" statement.
// If we explicitly put nil, like
// #"album_cover_photo_id": nil
// we get compiler error.
[albums addObject:album];
}
completionBlock(albums, nil);
}
}];
}

Answer 1

You wrote:
// Here an exception should be thrown but for some reason
// we just quit out of the method. Result would be the same if we put empty "return;" statement.
Most likely the exception is caught somewhere. Try putting a breakpoint on Objective-C exception throws (In Xcode, go to the Breakpoint tab, click + in the bottom left corner and select Add Exception Breakpoint. Make sure the parameters are set to Objective-C exception and break On Throw).

Answer 2

You claim that
NSString *albumID = dict[#"id"];
NSString *coverPhotoID = nil;
NSString *description = dict[#"description"];
NSString *name = dict[#"name"];
NSDictionary *album = #{#"album_id": albumID,
#"album_cover_photo_id": coverPhotoID,
#"album_description": description,
#"album_name": name };
doesn't crash your app.
Honestly, I don't believe it. Either you're trolling or you're misinterpreting whats happening.
As the first line of your for cycle log the dict dictionary:
NSLog(#"dict var: %#", dict);
Does dict contains the key album_cover_photo_id?
If you get something like
"album_cover_photo_id" : null
then NSString *coverPhotoID = dict[#"cover_photo"] is assigning an NSNull instance to coverPhotoID. In that case the app doesn't crash because an NSNull instance is not nil.
NSString *coverPhotoID = nil;
is different then
NSString *coverPhotoID = [NSNull null];
It's very common for servers to return nulls in JSON instead of omitting the key (server people are weird).
You can also log album after you create it
NSLog(#"album var: %#", album);
And if you are 100 % sure you're adding a nil to a dictionary, take it to the Apple developer forum. I bet they'd love to know about that bug.
I hope this helps you in some way.