Rails' nil?, for Objective-C

NSNullCheck.m

#import <Foundation/Foundation.h>

@interface NSObject (NSNullCheck)
- (BOOL)isNull;
@end

@implementation NSObject (NSNullCheck)
- (BOOL)isNull { return NO; }
@end

@implementation NSNull (NSNullCheck)
- (BOOL)isNull { return YES; }
@end

int main(int argc, char **argv)
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    NSString *s = @"My string";
    NSNull *n = [NSNull null];
    
    NSLog(@"s is null? %@ (should be NO)", [s isNull] ? @"YES" : @"NO");
    NSLog(@"n is null? %@ (should be YES)", [n isNull] ? @"YES" : @"NO");

    [pool release];
    return 0;
}