From bdcbad3fc957a73941e768ac2f30c4556c985965 Mon Sep 17 00:00:00 2001
From: Ben Johnson <benbjohnson@yahoo.com>
Date: Tue, 2 Oct 2018 13:17:54 -0600
Subject: [PATCH] Fix append of possible nil iterator.

This commit updates an iterator list to ignore `nil` iterators.
Adding a `nil` caused the `SeriesIterators.Close()` to panic.
---
 tsdb/index/tsi1/log_file.go | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tsdb/index/tsi1/log_file.go b/tsdb/index/tsi1/log_file.go
index 8316032b0c..a07de26d0a 100644
--- a/tsdb/index/tsi1/log_file.go
+++ b/tsdb/index/tsi1/log_file.go
@@ -343,7 +343,9 @@ func (f *LogFile) TagKeySeriesIDIterator(name, key []byte) tsdb.SeriesIDIterator
 		if tv.cardinality() == 0 {
 			continue
 		}
-		itrs = append(itrs, tsdb.NewSeriesIDSetIterator(tv.seriesIDSet()))
+		if itr := tsdb.NewSeriesIDSetIterator(tv.seriesIDSet()); itr != nil {
+			itrs = append(itrs, itr)
+		}
 	}
 
 	return tsdb.MergeSeriesIDIterators(itrs...)