chore: update output

Author: xshot9011

outputs.tf

@@ -1,6 +1,6 @@
 output "lb_public_dns" {
   description = "The DNS name of the public load balancer."
-  value       = aws_lb.public[0].dns_name
+  value       = try(aws_lb.public[0].dns_name, "")
 }
 
 output "lb_private_dns" {
@@ -9,7 +9,7 @@ output "lb_private_dns" {
 }
 
 output "vpn_public_dns" {
-  value       = try(aws_route53_record.public[0].name, aws_lb.public[0].dns_name)
+  value       = try(aws_route53_record.public[0].name, aws_lb.public[0].dns_name, [""])
   description = "public dns for connect vpn server"
 }