- (void)invokeDelegateItemsWithAction:(SEL)action withObjects:(id)firstObj, ... NS_REQUIRES_NIL_TERMINATION {
    NSMutableArray *deleteItems = [NSMutableArray arrayWithCapacity:0];
    NSSet *copySet = [NSSet setWithSet:self.delegateSet];
    for (MyDelegateItem *item in copySet) {
        if (item.delegate && [item.delegate respondsToSelector:action]) {
            NSMethodSignature *sigOfAction = [(id)item.delegate methodSignatureForSelector:action];
            NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:sigOfAction];
            [invocation setTarget:item.delegate];
            [invocation setSelector:action];

            if (firstObj) {
                NSInteger argsIndex = 2;
                va_list args;
                va_start(args, firstObj);

                id argObject = firstObj;
                while (argObject) {
                    if ([argObject isKindOfClass:[NSValue class]]) {
                        void *value;
                        [argObject getValue:&value];
                        [invocation setArgument:&value atIndex:argsIndex];
                    } else {
                        [invocation setArgument:&argObject atIndex:argsIndex];
                    }
                    argObject = va_arg(args, id);
                    argsIndex++;
                }
                va_end(args);
            }
            [invocation invoke];
        }
        if (!item.delegate) {
            [deleteItems addObject:item];
        }
    }
    for (id obj in deleteItems) {
        [self.delegateSet removeObject:obj];
    }
}