Intermittent Crash: - setObjectForKey: Object cannot be nil (key:ref_id)

Question

The ref_id object is string/number in the JSON response. Same code works most of the time. But sometime it crashes (~less than 5%).

      NSDictionary *udfDict = nil;
        if (data) {
            if ([data length] > 0) {
                udfDict = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:&serializationError];
            }
        }

        if (udfDict) {
            NSString *transactionreason;
            NSString *refId;
            if (![CustomUtilities isEmptyOrNull:udfDict[@"ref_id"]]) {

                refId = udfDict[@"ref_id"];
                [dict setObject:refId forKey:@"ref_id"];
}

Concern: If its not able to downcast from number to string, the code should break all the time.But thats not the case.The crash is intermittent and only code breaks for ~5% occurances.

Answer 1

The test whether data != nil is unnecessary. But do yourself and the readers of your code a favour and write if (data != nil) and not if (data). That's barbaric. Same for udfDict. length is a property, so data.length not [data length]. Why are you reading mutable containers? Is this some code that you copied and didn't understand?

Your code will crash if the JSON data is an array.

We don't know what isEmptyOrNull does.

Why setObject and not dict [@"ref_id"] = ... ?

And I don't see any numbers here. What's the actual problem?