cmd/utils: allow empty bootnodes flag override (#18509)

cmd/utils/flags.go

@@ -749,6 +749,7 @@ func setBootstrapNodes(ctx *cli.Context, cfg *p2p.Config) {
 
 	cfg.BootstrapNodes = make([]*enode.Node, 0, len(urls))
 	for _, url := range urls {
+		if url != "" {
 			node, err := enode.ParseV4(url)
 			if err != nil {
 				log.Crit("Bootstrap URL invalid", "enode", url, "err", err)
@@ -756,6 +757,7 @@ func setBootstrapNodes(ctx *cli.Context, cfg *p2p.Config) {
 			cfg.BootstrapNodes = append(cfg.BootstrapNodes, node)
 		}
 	}
+}
 
 // setBootstrapNodesV5 creates a list of bootstrap nodes from the command line
 // flags, reverting to pre-configured ones if none have been specified.