From 9a75b5f84b01b891c7a2c6a003c3be8b83d97bcd Mon Sep 17 00:00:00 2001
From: Krasi Georgiev <8903888+krasi-georgiev@users.noreply.github.com>
Date: Mon, 20 Jul 2020 18:23:18 +0300
Subject: [PATCH] Avoid panic when the headChunk is nil during isolation.

Signed-off-by: Krasi Georgiev <8903888+krasi-georgiev@users.noreply.github.com>
---
 tsdb/head.go | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/tsdb/head.go b/tsdb/head.go
index 0a16671ea..536487a2f 100644
--- a/tsdb/head.go
+++ b/tsdb/head.go
@@ -2186,10 +2186,8 @@ func (s *memSeries) iterator(id int, isoState *isolationState, chunkDiskMapper *
 				previousSamples += int(d.numSamples)
 			}
 		}
-		// mmappedChunks does not contain the last chunk. Hence check it separately.
-		if len(s.mmappedChunks) < ix {
-			previousSamples += s.headChunk.chunk.NumSamples()
-		} else {
+
+		if s.headChunk != nil {
 			totalSamples += s.headChunk.chunk.NumSamples()
 		}