diff --git a/server/src/test/java/org/elasticsearch/indices/IndicesRequestCacheTests.java b/server/src/test/java/org/elasticsearch/indices/IndicesRequestCacheTests.java
index 90806f85f7a47..590dc72e2a72b 100644
--- a/server/src/test/java/org/elasticsearch/indices/IndicesRequestCacheTests.java
+++ b/server/src/test/java/org/elasticsearch/indices/IndicesRequestCacheTests.java
@@ -601,7 +601,7 @@ public BytesRef toBytesRef() {
 
         @Override
         public BytesRefIterator iterator() {
-            return null;
+            return BytesRefIterator.EMPTY;
         }
 
         @Override