Objective-C stable multi-key sort with nulls last

#import <Foundation/Foundation.h>

static NSArray<NSDictionary *> *SortRecords(NSArray<NSDictionary *> *records) {
    NSMutableArray<NSNumber *> *order = [NSMutableArray array];
    for (NSUInteger i = 0; i < records.count; i++) [order addObject:@(i)];
    [order sortUsingComparator:^NSComparisonResult(NSNumber *ia, NSNumber *ib) {
        NSDictionary *a = records[ia.unsignedIntegerValue], *b = records[ib.unsignedIntegerValue];
        id an = a[@"name"], bn = b[@"name"];
        if (an || bn) {
            if (!an) return NSOrderedDescending; // nulls last
            if (!bn) return NSOrderedAscending;
            NSComparisonResult r = [an compare:bn options:NSCaseInsensitiveSearch];
            if (r != NSOrderedSame) return r;
            NSComparisonResult byAge = [(a[@"age"] ?: @0) compare:(b[@"age"] ?: @0)];
            if (byAge != NSOrderedSame) return byAge;
        }
        return [ia compare:ib]; // original index keeps ties stable
    }];
    NSMutableArray *out = [NSMutableArray array];
    for (NSNumber *i in order) [out addObject:records[i.unsignedIntegerValue]];
    return out;
}