A crashy piece of code under ARC

gistfile1.m

- (void)dwk_postChangeNotification:(NSString *)notificationName newValue:(id)newValue oldValue:(id)oldValue
{
	if (CBIsEmpty(newValue) || CBIsEmpty([self fileModificationDate])) {
            return;
        }
	
	NSMutableDictionary *userInfo = [NSMutableDictionary dictionaryWithCapacity:2];
	
	[userInfo setObject:newValue forKey:kNotificationOldValueKey];
	
	if (CBIsNotEmpty(oldValue)) {
            [userInfo setObject:oldValue forKey:kNotificationNewValueKey];
        }
	
	NSNotification *changeNotification = [NSNotification notificationWithName:notificationName object:self userInfo:userInfo];
	
	void (^saveCompletionHandler)(BOOL) = [^(BOOL success) {
            [[NSNotificationCenter defaultCenter] postNotification:changeNotification];
	} copy];
	
	// The document has unsaved changes
	if (UIDocumentStateNormal != [self documentState]) {
            saveCompletionHandler (YES);
	} else {
            [[DWKDocumentsController sharedController] saveDocumentToDisk:self completionHandler:saveCompletionHandler];
	}
}