chore(middleware/metrics): if requests and seconds are nil, return directly (#3298)

Author: Ccheers

middleware/metrics/metrics.go

@@ -100,6 +100,11 @@ func Server(opts ...Option) middleware.Middleware {
 	}
 	return func(handler middleware.Handler) middleware.Handler {
 		return func(ctx context.Context, req interface{}) (interface{}, error) {
+			// if requests and seconds are nil, return directly
+			if op.requests == nil && op.seconds == nil {
+				return handler(ctx, req)
+			}
+
 			var (
 				code      int
 				reason    string