From f7cb1d4d084b81a73b360c669d28576168710d75 Mon Sep 17 00:00:00 2001
From: Julie Tibshirani <julie.tibshirani@elastic.co>
Date: Fri, 20 Aug 2021 10:28:00 -0700
Subject: [PATCH] [7.x] Make sure copy_to accepts null values (#76770)

In #72820 we improved the error message when attempting to `copy_to` with an
object value. The change accidentally started throwing errors for null values
too, although they're allowed. This PR fixes the regression and adds an
explicit test for `copy_to` with null values.
---
 .../index/mapper/DocumentParser.java          |  2 +-
 .../index/mapper/CopyToMapperTests.java       | 26 +++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/server/src/main/java/org/elasticsearch/index/mapper/DocumentParser.java b/server/src/main/java/org/elasticsearch/index/mapper/DocumentParser.java
index 6c9f15c85bb9c..5512f216ac2e7 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/DocumentParser.java
+++ b/server/src/main/java/org/elasticsearch/index/mapper/DocumentParser.java
@@ -556,7 +556,7 @@ static void parseObjectOrField(DocumentParserContext context, Mapper mapper) thr
             List<String> copyToFields = fieldMapper.copyTo().copyToFields();
             if (context.isWithinCopyTo() == false && copyToFields.isEmpty() == false) {
                 XContentParser.Token currentToken = context.parser().currentToken();
-                if (currentToken.isValue() == false) {
+                if (currentToken.isValue() == false && currentToken != XContentParser.Token.VALUE_NULL) {
                     // sanity check, we currently support copy-to only for value-type field, not objects
                     throw new MapperParsingException("Cannot copy field [" + mapper.name() + "] to fields " + copyToFields +
                         ". Copy-to currently only works for value-type fields, not objects.");
diff --git a/server/src/test/java/org/elasticsearch/index/mapper/CopyToMapperTests.java b/server/src/test/java/org/elasticsearch/index/mapper/CopyToMapperTests.java
index 27f7ebf4aeaeb..7ed078c0ca5ff 100644
--- a/server/src/test/java/org/elasticsearch/index/mapper/CopyToMapperTests.java
+++ b/server/src/test/java/org/elasticsearch/index/mapper/CopyToMapperTests.java
@@ -13,6 +13,7 @@
 import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentParser;
+import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.common.xcontent.json.JsonXContent;
 import org.hamcrest.Matchers;
 
@@ -644,6 +645,31 @@ public void testCopyToDateRangeFailure() throws Exception {
         );
     }
 
+    public void testCopyToWithNullValue() throws Exception {
+        DocumentMapper docMapper = createDocumentMapper(topMapping(b ->
+            b.startObject("properties")
+                .startObject("keyword_copy")
+                    .field("type", "keyword")
+                    .field("null_value", "default-value")
+                .endObject()
+                .startObject("keyword")
+                    .field("type", "keyword")
+                    .array("copy_to", "keyword_copy")
+                .endObject()
+            .endObject()));
+
+        BytesReference json = BytesReference.bytes(jsonBuilder().startObject()
+                .nullField("keyword")
+            .endObject());
+
+        LuceneDocument document = docMapper.parse(new SourceToParse("test", MapperService.SINGLE_MAPPING_NAME,
+            "1", json, XContentType.JSON)).rootDoc();
+        assertEquals(0, document.getFields("keyword").length);
+
+        IndexableField[] fields = document.getFields("keyword_copy");
+        assertEquals(2, fields.length);
+    }
+
     public void testCopyToGeoPoint() throws Exception {
         DocumentMapper docMapper = createDocumentMapper(topMapping(b -> {
                 b.startObject("properties");