-[NSNull length]: unrecognized selector sent to JSON objects

Question

I\'m developing an iOS 5.0+ app with latest SDK.

I get a very strange error with this code:

- (NSMutableURLRequest*)setupRequestWithService:(NSString         


        

Answer 1

In line with David H's answer, how about a category on NSNull that just uses ObjC's message forwarding to "do nothing", to emulate the runtime's behavior when sending messages to nil?

Like this:

@interface NSNull (ForwardInvocation)

@end

@implementation NSNull (ForwardInvocation)

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
    return [NSNull methodSignatureForSelector:@selector(description)];
}

- (void)forwardInvocation:(NSInvocation *)anInvocation {
    // do nothing; prevent 'unrecognized selector' crashes
}

@end

The [NSNull methodSignatureForSelector:@selector(description)]; takes advantage of the fact that NSNull inherits from NSObject, which provides the description method. This satisfies the forwarding mechanism requirement for implementing -methodSignatureForSelector:.