From b7bac252ba10d2747ed775cc7b2e5008026b3859 Mon Sep 17 00:00:00 2001
From: Alan Woodward <romseygeek@apache.org>
Date: Fri, 29 Nov 2019 10:32:57 +0000
Subject: [PATCH] Fix BWC assertion in GetFieldMappingsResponse (#49706)

Closes #49702
---
 .../indices/mapping/get/GetFieldMappingsResponse.java      | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsResponse.java b/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsResponse.java
index bd4fbc5f82af5..c57ebbb942f68 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsResponse.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsResponse.java
@@ -36,6 +36,7 @@
 
 import java.io.IOException;
 import java.io.InputStream;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Objects;
@@ -66,7 +67,11 @@ public class GetFieldMappingsResponse extends ActionResponse implements ToXConte
             String index = in.readString();
             if (in.getVersion().before(Version.V_8_0_0)) {
                 int typesSize = in.readVInt();
-                assert typesSize == 1;
+                assert typesSize == 1 || typesSize == 0 : "Expected 0 or 1 types but got " + typesSize;
+                if (typesSize == 0) {
+                    indexMapBuilder.put(index, Collections.emptyMap());
+                    continue;
+                }
                 in.readString(); // type
             }
             int fieldSize = in.readVInt();