Recursively remove NSNull instances

gistfile1.m

// Use case being removing null values from the results of JSON encoding (thus only supports dictionaries and arrays)
__block id (^removeNull)(id) = ^(id rootObject) {
    // Recurse through dictionaries
    if ([rootObject isKindOfClass:[NSDictionary class]]) {
        NSMutableDictionary *sanitizedDictionary = [NSMutableDictionary dictionaryWithDictionary:rootObject];
        [rootObject enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
            id sanitized = removeNull(obj);
            if (!sanitized) {
                [sanitizedDictionary removeObjectForKey:key];
            } else {
                [sanitizedDictionary setObject:sanitized forKey:key];
            }
        }];
        
        return [NSDictionary dictionaryWithDictionary:sanitizedDictionary];
    }
    
    // Recurse through arrays
    if ([rootObject isKindOfClass:[NSArray class]]) {
        NSMutableArray *sanitizedArray = [NSMutableArray arrayWithArray:rootObject];
        [rootObject enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
            id sanitized = removeNull(obj);
            if (!sanitized) {
                [sanitizedArray removeObjectIdenticalTo:obj];
            } else {
                [sanitizedArray replaceObjectAtIndex:[sanitizedArray indexOfObject:obj] withObject:sanitized];
            }
        }];
        
        return [NSArray arrayWithArray:sanitizedArray];
    }
    
    // Base case
    if ([rootObject isKindOfClass:[NSNull class]]) {
        return (id)nil;
    } else {
        return rootObject;
    }
};

Xcode warning on line 7:

Capturing 'removeNull' strongly in this block is likely to lead to a retain cycle