use coalesce

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

Author: doublethink13

main.tf

@@ -16,8 +16,11 @@ locals {
 
   userdata = templatefile("${path.module}/userdata.sh.tmpl", {
     authkey           = try(
-      one(tailscale_oauth_client.default[*].key), 
-      one(tailscale_tailnet_key.default[*].key)
+      coalesce(
+        one(tailscale_oauth_client.default[*].key),
+        one(tailscale_tailnet_key.default[*].key),
+      ),
+      null
     )
     exit_node_enabled = var.exit_node_enabled
     hostname          = module.this.id