if statement for dictionary objectforkey:@"key" when value is <null>
objective-c
Solution
You have an instance of `NSNull`. Actually, the instance, since it's a singleton.
Cocoa collections can't contain `nil`, although they may return `nil` if you try to access something which isn't present.
However, sometimes it's valuable for a program to store a thing meaning "nothing" in a collection. That's what `NSNull` is for.
As it happens, JSON can represent null objects. So, when converting JSON to a Cocoa collection, those null objects get translated into the `NSNull` object.
When Cocoa formats a string with a "%@" specifier, a `nil` value will get formatted as "(null)" with parentheses. An `NSNull` value will get formatted as "<null>" with angle brackets.
Problem
I am working with objective c for an iphone app. I see that `[dictionary objectForKey:@"key"]` return `<null>`. Doing a `if([dictionary objectForKey:@"key"] == nil || [dictionary objectForKey:@"key"] == null)` does not seem to catch this case. Doing a `if([[dictionary objectForKey:@"key"] isEqualToString:@"<null>"])` causes my program to crash. What is the correct expression to catch `<null>`? More Details An if statement for nil still isn't catching the case... Maybe i'm just too tired to see something, but here's additional info: Dictionary is populated via a url that contains json data like so: ``` NSURL *url = [NSURL URLWithString:"http://site.com/"]; dataresult = [NSData dataWithContentsOfURL:url]; NSError *error; NSMutableDictionary *dictionary = [NSJSONSerialization JSONObjectWithData:dataresult options:kNilOptions error:& error]; ``` doing an NSLog on the dictionary gives this output: ``` { key = "<null>"; responseMessage = "The email / registration code combination is incorrect"; } ```