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In our project, we occasionally get our iPhone app to crash when there is something on the network returns JSON with nil in it. Of course, we do have a helper class, which takes care of problems like that. However, people are error-prone and do call objectForKey on NSDictionary instead of our own stringForKey or dateForKey etc.. Now, there is a class to kill all problems like that, once and for all: https://github.com/nicklockwood/NullSafe

My question is: Is NullSafe is really safe? Because sometimes you do want your program to crash if the logic is wrong and you get NSNull. Just ignoring the problem hides it. The app probably will not crash, but, in some cases, will do something weird.

Now I am leaning towards not using this class and just making sure that our JSON NSDictionaries is filtered of all NSNulls BEFORE we try to parse get the values (It could affect performance though).

What do you guys think?

mutable.me
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    Seems to me that, since you don't really know what types JSON has returned, it's better to simply use isKindOfClass to check what's in front of you before you step in it. – Hot Licks Jan 28 '13 at 21:56
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    _(The other guy here removed his comments, so I removed mine. It was like talking to nobody.)_ – Tricertops Jan 28 '13 at 22:43

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That class is safe in terms of not crashing the application when you send some message to it. It behaves much like nil value.

This class does not solve bugs! If you may get NSNull you should act as it is there and handle that case.

Once I used such class (also because of JSON), but I put NSLog (or ratcher breakpoint) into the -forwardInvocation: method to see from where and why it was called. I wouldn't use this in production.

You also asked about performance. Not sure what takes more: removing NSNulls from an array or searching all classes for their method signatures ;)

Tricertops
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  • It does solve a bug. Nil in json should be nil. NSNull should be nil. – Tom Andersen Sep 28 '13 at 12:41
  • It's definitely not safe and may introduce another bugs. Object that is non-nil and returns nil for _any_ method will make problems later. – Tricertops Sep 28 '13 at 16:11
  • No, JSON null shouldn't be nil. nil represents "it's not there". [NSNull null] represents "it's there, but it doesn't have a value". – gnasher729 Jul 31 '14 at 22:15