--- sys/geom/vinum/geom_vinum_list.c	2008-11-22 17:01:17.000000000 +0800
+++ /var/current/mysrc/sys/geom/vinum/geom_vinum_list.c	2008-11-23 21:05:29.000000000 +0800
@@ -69,7 +69,10 @@
 
 	/* Figure out which command was given. */
 	cmd = gctl_get_param(req, "cmd", NULL);
-
+	if (cmd == NULL) {
+		gctl_error(req, "cmd missing");
+		return;
+	}
 	/* List specific objects or everything. */
 	if (!strcmp(cmd, "list") || !strcmp(cmd, "l")) {
 		if (*argc) {