CFRelease crash

Crash on CFRelease(res)

    {
        dispatch_block_t block = ^{
            //All this dancing is an attempt to work around some weird crash:
            //seems like ARC is trying to release NULL before assigning new value
            CFDictionaryRef res = SCDynamicStoreCopyMultiple(store, NULL, keyPatterns);
            if (res && store) {
                NSDictionary *nsRes = (__bridge_transfer NSDictionary *)CFPropertyListCreateDeepCopy(kCFAllocatorDefault,
                                                                                                     (CFPropertyListRef)res,
                                                                                                     kCFPropertyListImmutable);
                setDynamicStore(nsRes);
            } else {
                ZLogError("SCU:[%s]%s refreshDynamicStore failed",
                          dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL),
                          __FUNCTION__);
                setDynamicStore(NULL);
            }
            if(res) {
                CFRelease(res);
            }
        };
        if (dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL) == dispatch_queue_get_label(queue)) {
            block();
        } else {
            dispatch_async(queue, block);
        }
    }