From ff831719090765ac2d4a21251869d1344290df7c Mon Sep 17 00:00:00 2001
From: Simon Marsh <simon@sesa.me.uk>
Date: Thu, 11 Jul 2019 09:09:12 +0100
Subject: [PATCH] Fix case where a master isn't available

---
 dns.go | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/dns.go b/dns.go
index fab5fe1..43043f0 100644
--- a/dns.go
+++ b/dns.go
@@ -243,10 +243,13 @@ func (m *DNSMetrics) Collect() {
 
 	for ix, server := range dns_servers {
 		if server.role == "master" {
-			soa := results[ix].serial
-			masters = append(masters, soa)
-			if soa > latest_soa {
-				latest_soa = soa
+			// check that a result was actually received by the master
+			if results[ix] != nil {
+				soa := results[ix].serial
+				masters = append(masters, soa)
+				if soa > latest_soa {
+					latest_soa = soa
+				}
 			}
 		}
 	}