Swap partitions may have neither label nor uuid
--- busybox-1.20.0/util-linux/volume_id/get_devname.c
+++ busybox-1.20.0/util-linux/volume_id/get_devname.c
@@ -46,10 +46,7 @@
 	if (ioctl(/*vid->*/fd, BLKGETSIZE64, &size) != 0)
 		size = 0;
 
-	if (volume_id_probe_all(vid, /*0,*/ size) != 0)
-		goto ret;
-
-	if (vid->label[0] != '\0' || vid->uuid[0] != '\0') {
+	if (volume_id_probe_all(vid, /*0,*/ size) == 0) {
 		*label = xstrndup(vid->label, sizeof(vid->label));
 		*uuid  = xstrndup(vid->uuid, sizeof(vid->uuid));
 #if ENABLE_FEATURE_BLKID_TYPE
--- busybox-1.20.0/util-linux/volume_id/volume_id.c
+++ busybox-1.20.0/util-linux/volume_id/volume_id.c
@@ -192,6 +192,7 @@
 			goto ret;
 	}
 
+	id->error = 1;
  ret:
 	volume_id_free_buffer(id);
 	return (- id->error); /* 0 or -1 */