Fix store null values implementation.

src/main/java/org/springframework/data/elasticsearch/client/elc/ElasticsearchClients.java

@@ -35,6 +35,9 @@
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
 import org.apache.http.*;
 import org.apache.http.client.config.RequestConfig;
 import org.apache.http.entity.ByteArrayEntity;
@@ -269,7 +272,14 @@ private static ElasticsearchTransport getElasticsearchTransport(RestClient restC
 		TransportOptions transportOptionsWithHeader = transportOptionsBuilder
 				.addHeader(X_SPRING_DATA_ELASTICSEARCH_CLIENT, clientType).build();
 
-		return new RestClientTransport(restClient, new JacksonJsonpMapper(), transportOptionsWithHeader);
+		// we need to create our own objectMapper that keeps null values in order to provide the storeNullValue
+		// functionality. The one Elasticsearch would provide removes the nulls. We remove unwanted nulls before they get
+		// into this mapper, so we can safely keep them here.
+		var objectMapper = (new ObjectMapper())
+				.configure(SerializationFeature.INDENT_OUTPUT, false)
+				.setSerializationInclusion(JsonInclude.Include.ALWAYS);
+
+		return new RestClientTransport(restClient, new JacksonJsonpMapper(objectMapper), transportOptionsWithHeader);
 	}
 
 	private static List<String> formattedHosts(List<InetSocketAddress> hosts, boolean useSsl) {

src/test/java/org/springframework/data/elasticsearch/client/elc/ELCWiremockTests.java

@@ -0,0 +1,140 @@
+/*
+ * Copyright 2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.elasticsearch.client.elc;
+
+import static com.github.tomakehurst.wiremock.client.WireMock.*;
+import static com.github.tomakehurst.wiremock.core.WireMockConfiguration.*;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.junit.jupiter.api.extension.RegisterExtension;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.data.annotation.Id;
+import org.springframework.data.elasticsearch.annotations.Document;
+import org.springframework.data.elasticsearch.annotations.Field;
+import org.springframework.data.elasticsearch.client.ClientConfiguration;
+import org.springframework.data.elasticsearch.core.ElasticsearchOperations;
+import org.springframework.lang.Nullable;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+import com.github.tomakehurst.wiremock.junit5.WireMockExtension;
+
+/**
+ * Tests that need to check the data produced by the Elasticsearch client
+ * @author Peter-Josef Meisch
+ */
+@ExtendWith(SpringExtension.class)
+public class ELCWiremockTests {
+
+	@RegisterExtension static WireMockExtension wireMock = WireMockExtension.newInstance()
+			.options(wireMockConfig()
+					.dynamicPort()
+					// needed, otherwise Wiremock goes to test/resources/mappings
+					.usingFilesUnderDirectory("src/test/resources/wiremock-mappings"))
+			.build();
+
+	@Configuration
+	static class Config extends ElasticsearchConfiguration {
+		@Override
+		public ClientConfiguration clientConfiguration() {
+			return ClientConfiguration.builder()
+					.connectedTo("localhost:" + wireMock.getPort())
+					.build();
+		}
+	}
+
+	@Autowired ElasticsearchOperations operations;
+
+	@Test // #2839
+	@DisplayName("should store null values if configured")
+	void shouldStoreNullValuesIfConfigured() {
+
+		wireMock.stubFor(put(urlPathEqualTo("/null-fields/_doc/42"))
+				.withRequestBody(equalToJson("""
+						{
+							"_class": "org.springframework.data.elasticsearch.client.elc.ELCWiremockTests$EntityWithNullFields",
+							"id": "42",
+							"field1": null
+							}
+						"""))
+				.willReturn(
+						aResponse()
+								.withStatus(200)
+								.withHeader("X-elastic-product", "Elasticsearch")
+								.withHeader("content-type", "application/vnd.elasticsearch+json;compatible-with=8")
+								.withBody("""
+										{
+										  "_index": "null-fields",
+										  "_id": "42",
+										  "_version": 1,
+										  "result": "created",
+										  "forced_refresh": true,
+										  "_shards": {
+										    "total": 2,
+										    "successful": 1,
+										    "failed": 0
+										  },
+										  "_seq_no": 1,
+										  "_primary_term": 1
+										}
+										""")));
+
+		var entity = new EntityWithNullFields();
+		entity.setId("42");
+
+		operations.save(entity);
+		// no need to assert anything, if the field1:null is not sent, we run into a 404 error
+	}
+
+	@Document(indexName = "null-fields")
+	static class EntityWithNullFields {
+		@Nullable
+		@Id private String id;
+		@Nullable
+		@Field(storeNullValue = true) private String field1;
+		@Nullable
+		@Field private String field2;
+
+		@Nullable
+		public String getId() {
+			return id;
+		}
+
+		public void setId(@Nullable String id) {
+			this.id = id;
+		}
+
+		@Nullable
+		public String getField1() {
+			return field1;
+		}
+
+		public void setField1(@Nullable String field1) {
+			this.field1 = field1;
+		}
+
+		@Nullable
+		public String getField2() {
+			return field2;
+		}
+
+		public void setField2(@Nullable String field2) {
+			this.field2 = field2;
+		}
+	}
+}