How to deal with NSNull

"somevalue": "<null>"

Sometimes when we receive the above JSON from server side, when we parse the JSON we will get NSNull. If we call a method on this object, the app will crash and generate the following error for example.

-[NSNull length]: unrecognized selector sent to instance 0x388a4a70

in order to prevent this, we have several solutions

• there is a property called removesKeysWithNullValues in AFNetworking. If we set it to YES, all the NSNull will become nil and we can use it without crash.

((AFJSONResponseSerializer *)manager.responseSerializer).removesKeysWithNullValues = YES;

• use the method AFJSONObjectByRemovingKeysWithNullValues originated from here

id AFJSONObjectByRemovingKeysWithNullValues(id JSONObject, NSJSONReadingOptions readingOptions) {
    if ([JSONObject isKindOfClass:[NSArray class]]) {
        NSMutableArray *mutableArray = [NSMutableArray arrayWithCapacity:[(NSArray *)JSONObject count]];
        for (id value in (NSArray *)JSONObject) {
            if (![value isEqual:[NSNull null]]) {
                [mutableArray addObject:AFJSONObjectByRemovingKeysWithNullValues(value, readingOptions)];
            }
        }

        return (readingOptions & NSJSONReadingMutableContainers) ? mutableArray : [NSArray arrayWithArray:mutableArray];
    } else if ([JSONObject isKindOfClass:[NSDictionary class]]) {
        NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionaryWithDictionary:JSONObject];
        for (id <NSCopying> key in [(NSDictionary *)JSONObject allKeys]) {
            id value = (NSDictionary *)JSONObject[key];
            if (!value || [value isEqual:[NSNull null]]) {
                [mutableDictionary removeObjectForKey:key];
            } else if ([value isKindOfClass:[NSArray class]] || [value isKindOfClass:[NSDictionary class]]) {
                mutableDictionary[key] = AFJSONObjectByRemovingKeysWithNullValues(value, readingOptions);
            }
        }

        return (readingOptions & NSJSONReadingMutableContainers) ? mutableDictionary : [NSDictionary dictionaryWithDictionary:mutableDictionary];
    }

    return JSONObject;
}