Weak linking with extern NSString *const issue

WeakExternCrash.m

#import <Social/Social.h>

/* Compiled with iOS 6 SDK
 * Social.framework weak linked (Optional)
 * Run on iOS 5.1 (simulator and device)
 */

// http://simx.me/technonova/software_development/checking_for_weak_linked_frameworks.html
//http://developer.apple.com/library/mac/documentation/MacOSX/Conceptual/BPFrameworks/Concepts/WeakLinking.html#//apple_ref/doc/uid/20002378-106633-CJBGFCAC

extern NSString *const SLServiceTypeFacebook __attribute__((weak_import));

int main(int argc, char *argv[])
{
	@autoreleasepool
	{
		NSLog(@"%p", &SLServiceTypeFacebook);
		BOOL symbolExists = (&SLServiceTypeFacebook != NULL);
		if (symbolExists)
		{
			NSString *serviceType = SLServiceTypeFacebook;
			NSLog(@"serviceType %@", serviceType);
		}
		NSLog(@"Didn't crash");
	}
	return 0;
}