Try to return an Option[String] with review suggestions

metrics/opentelemetry-metrics/src/main/scala/sttp/tapir/server/metrics/opentelemetry/OpenTelemetryMetrics.scala

@@ -49,15 +49,16 @@ object OpenTelemetryMetrics {
       "url.scheme" -> { case (_, req) => req.uri.scheme.getOrElse("unknown") },
       "path" -> { case (ep, _) => ep.showPathTemplate(showQueryParam = None) }
     ),
-    forResponse = List(
-      "http.response.status_code" -> {
-        case Right(r) => r.code.code.toString
-        // Default to 500 for exceptions
-        case Left(_) => "500"
-      },
-      "error.type" -> {
-        case Left(ex) => ex.getClass.getSimpleName
-        case Right(_) => ""
+  forResponse = List(
+    "http.response.status_code" -> {
+      case Right(r) => Some(r.code.code.toString) 
+      case Left(_) => Some("500") 
+    },
+    "error.type" -> {
+      case Left(ex) => Some(ex.getClass.getName) 
+      case Right(_) => None 
+    }
+  ).collect { case (k, Some(v)) => k -> v }
 
       }
     )