fix coredump, register default cluster name

cmd/cluster.go

@@ -194,6 +194,12 @@ func ClusterSettingsSet(conf *cfg.Config) *cli.Command {
 		},
 
 		Action: func(ctx context.Context, cmd *cli.Command) error {
+			args := cmd.Args()
+
+			if args.Len() == 0 {
+				return errors.New("at least one setting must be specified (format: setting:value)")
+			}
+
 			if err := es.ClusterSettingsSet(conf, cmd.Args()); err != nil {
 				return err
 			}