root name is "." instead of ""

src/vmm_core.ml

@@ -66,7 +66,9 @@ module Name = struct
         | _ -> false)
       s (* only LDH (letters, digits, hyphen)! *)
 
-  let to_string ids = String.concat ~sep:"." ids
+  let to_string = function
+    | [] -> "."
+    | ids -> String.concat ~sep:"." ids
 
   let to_list x = x
 

src/vmm_resources.ml

@@ -83,7 +83,7 @@ let unikernel_metrics =
 
 let rec report_vms t name =
   let name' = Name.drop name in
-  let str = if Name.is_root name' then "." else Name.to_string name' in
+  let str = Name.to_string name' in
   Metrics.add unikernel_metrics (fun x -> x str) (fun d -> d (t, name'));
   if Name.is_root name' then () else report_vms t name'