Allow [null] values in [null_value] (#61798)

Several field mappers have a null_value parameter, that allows you to specify a placeholder
value to insert into a document if the incoming value for that field is null. The default value
for this is always null, meaning "add no placeholder". However, we explicitly bar users from
setting this parameter directly to null (done in #7978, in order to fix an NPE).

This exclusion means that if a mapper is serialized with include_defaults, then we either need
to special-case null_value to ensure that it is not output when it holds the default value, or
we find that the resulting serialized form cannot be used to create a mapping. This stops us
doing some useful generic testing of mappers.

This commit permits null as a parameter value for null_value, and changes the tests to check
that it is a) permissible and b) applied without throwing errors. As part of the testing changes,
a new base class MapperServiceTestCase is refactored from MapperTestCase, holding
the various helper methods related to building mappings but not the single-mapper specific
abstract methods.

Closes #58823

server/src/main/java/org/elasticsearch/index/mapper/AbstractPointGeometryFieldMapper.java

@@ -96,9 +96,6 @@ public abstract class AbstractPointGeometryFieldMapper<Parsed, Processed> extend
                 Object propNode = entry.getValue();
 
                 if (Names.NULL_VALUE.match(propName, LoggingDeprecationHandler.INSTANCE)) {
-                    if (propNode == null) {
-                        throw new MapperParsingException("Property [null_value] cannot be null.");
-                    }
                     nullValue = propNode;
                     iterator.remove();
                 }
@@ -146,7 +143,7 @@ public abstract class AbstractPointGeometryFieldMapper<Parsed, Processed> extend
     @Override
     public void doXContentBody(XContentBuilder builder, boolean includeDefaults, Params params) throws IOException {
         super.doXContentBody(builder, includeDefaults, params);
-        if (nullValue != null) {
+        if (nullValue != null || includeDefaults) {
             builder.field(Names.NULL_VALUE.getPreferredName(), nullValue);
         }
     }

server/src/main/java/org/elasticsearch/index/mapper/BooleanFieldMapper.java

@@ -82,7 +82,8 @@ public class BooleanFieldMapper extends ParametrizedFieldMapper {
         private final Parameter<Boolean> stored = Parameter.storeParam(m -> toType(m).stored, false);
 
         private final Parameter<Boolean> nullValue = new Parameter<>("null_value", false, () -> null,
-            (n, c, o) -> XContentMapValues.nodeBooleanValue(o), m -> toType(m).nullValue);
+            (n, c, o) -> o == null ? null : XContentMapValues.nodeBooleanValue(o), m -> toType(m).nullValue)
+            .acceptsNull();
 
         private final Parameter<Float> boost = Parameter.boostParam();
         private final Parameter<Map<String, String>> meta = Parameter.metaParam();

server/src/main/java/org/elasticsearch/index/mapper/DateFieldMapper.java

@@ -195,7 +195,7 @@ public final class DateFieldMapper extends ParametrizedFieldMapper {
             (n, c, o) -> LocaleUtils.parse(o.toString()), m -> toType(m).locale);
 
         private final Parameter<String> nullValue
-            = Parameter.stringParam("null_value", false, m -> toType(m).nullValueAsString, null);
+            = Parameter.stringParam("null_value", false, m -> toType(m).nullValueAsString, null).acceptsNull();
         private final Parameter<Boolean> ignoreMalformed;
 
         private final Resolution resolution;

server/src/main/java/org/elasticsearch/index/mapper/IpFieldMapper.java

@@ -68,14 +68,15 @@ public class IpFieldMapper extends ParametrizedFieldMapper {
 
         private final Parameter<Boolean> ignoreMalformed;
         private final Parameter<InetAddress> nullValue = new Parameter<>("null_value", false, () -> null,
-            (n, c, o) -> InetAddresses.forString(o.toString()), m -> toType(m).nullValue)
+            (n, c, o) -> o == null ? null : InetAddresses.forString(o.toString()), m -> toType(m).nullValue)
             .setSerializer((b, f, v) -> {
                 if (v == null) {
                     b.nullField(f);
                 } else {
                     b.field(f, InetAddresses.toAddrString(v));
                 }
-            }, NetworkAddress::format);
+            }, NetworkAddress::format)
+            .acceptsNull();
 
         private final Parameter<Map<String, String>> meta = Parameter.metaParam();
 

server/src/main/java/org/elasticsearch/index/mapper/KeywordFieldMapper.java

@@ -86,7 +86,8 @@ public final class KeywordFieldMapper extends ParametrizedFieldMapper {
         private final Parameter<Boolean> hasDocValues = Parameter.docValuesParam(m -> toType(m).hasDocValues, true);
         private final Parameter<Boolean> stored = Parameter.storeParam(m -> toType(m).fieldType.stored(), false);
 
-        private final Parameter<String> nullValue = Parameter.stringParam("null_value", false, m -> toType(m).nullValue, null);
+        private final Parameter<String> nullValue
+            = Parameter.stringParam("null_value", false, m -> toType(m).nullValue, null).acceptsNull();
 
         private final Parameter<Boolean> eagerGlobalOrdinals
             = Parameter.boolParam("eager_global_ordinals", true, m -> toType(m).eagerGlobalOrdinals, false);

server/src/main/java/org/elasticsearch/index/mapper/NumberFieldMapper.java

@@ -109,7 +109,7 @@ public class NumberFieldMapper extends ParametrizedFieldMapper {
             this.coerce
                 = Parameter.explicitBoolParam("coerce", true, m -> toType(m).coerce, coerceByDefault);
             this.nullValue = new Parameter<>("null_value", false, () -> null,
-                (n, c, o) -> type.parse(o, false), m -> toType(m).nullValue);
+                (n, c, o) -> o == null ? null : type.parse(o, false), m -> toType(m).nullValue).acceptsNull();
         }
 
         Builder nullValue(Number number) {

server/src/test/java/org/elasticsearch/index/mapper/NullValueTests.java

@@ -1,16 +1,3 @@
-package org.elasticsearch.index.mapper;
-
-import org.elasticsearch.common.Strings;
-import org.elasticsearch.common.compress.CompressedXContent;
-import org.elasticsearch.common.settings.Settings;
-import org.elasticsearch.common.xcontent.XContentFactory;
-import org.elasticsearch.index.IndexService;
-import org.elasticsearch.test.ESSingleNodeTestCase;
-
-import static org.hamcrest.Matchers.containsString;
-import static org.hamcrest.Matchers.either;
-import static org.hamcrest.Matchers.equalTo;
-
 /*
  * Licensed to Elasticsearch under one or more contributor
  * license agreements. See the NOTICE file distributed with
@@ -30,32 +17,33 @@ import static org.hamcrest.Matchers.equalTo;
  * under the License.
  */
 
-public class NullValueTests extends ESSingleNodeTestCase {
+package org.elasticsearch.index.mapper;
+
+import org.elasticsearch.common.Strings;
+import org.elasticsearch.common.xcontent.ToXContent;
+import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.common.xcontent.json.JsonXContent;
+
+import java.util.Map;
+
+import static org.hamcrest.Matchers.containsString;
+
+public class NullValueTests extends MapperServiceTestCase {
+
     public void testNullNullValue() throws Exception {
-        IndexService indexService = createIndex("test", Settings.builder().build());
+
         String[] typesToTest = {"integer", "long", "double", "float", "short", "date", "ip", "keyword", "boolean", "byte", "geo_point"};
 
         for (String type : typesToTest) {
-            String mapping = Strings.toString(XContentFactory.jsonBuilder()
-                    .startObject()
-                        .startObject("type")
-                            .startObject("properties")
-                                .startObject("numeric")
-                                    .field("type", type)
-                                    .field("null_value", (String) null)
-                                .endObject()
-                            .endObject()
-                        .endObject()
-                    .endObject());
-
-            try {
-                indexService.mapperService().documentMapperParser().parse("type", new CompressedXContent(mapping));
-                fail("Test should have failed because [null_value] was null.");
-            } catch (MapperParsingException e) {
-                assertThat(e.getMessage(),
-                    either(equalTo("Property [null_value] cannot be null."))
-                    .or(containsString("must not have a [null] value")));
-            }
+            DocumentMapper mapper = createDocumentMapper(fieldMapping(b -> b.field("type", type).nullField("null_value")));
+
+            mapper.parse(source(b -> b.nullField("field")));
+
+            ToXContent.Params params = new ToXContent.MapParams(Map.of("include_defaults", "true"));
+            XContentBuilder b = JsonXContent.contentBuilder().startObject();
+            mapper.mapping().toXContent(b, params);
+            b.endObject();
+            assertThat(Strings.toString(b), containsString("\"null_value\":null"));
         }
     }
 }

test/framework/src/main/java/org/elasticsearch/index/mapper/MapperServiceTestCase.java

@@ -0,0 +1,179 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you 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
+ *
+ *     http://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.elasticsearch.index.mapper;
+
+import org.apache.lucene.analysis.standard.StandardAnalyzer;
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.IndexWriterConfig;
+import org.apache.lucene.index.RandomIndexWriter;
+import org.apache.lucene.store.Directory;
+import org.elasticsearch.Version;
+import org.elasticsearch.cluster.metadata.IndexMetadata;
+import org.elasticsearch.common.CheckedConsumer;
+import org.elasticsearch.common.bytes.BytesReference;
+import org.elasticsearch.common.compress.CompressedXContent;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.common.xcontent.XContentFactory;
+import org.elasticsearch.common.xcontent.XContentType;
+import org.elasticsearch.common.xcontent.json.JsonXContent;
+import org.elasticsearch.index.IndexSettings;
+import org.elasticsearch.index.analysis.AnalyzerScope;
+import org.elasticsearch.index.analysis.IndexAnalyzers;
+import org.elasticsearch.index.analysis.NamedAnalyzer;
+import org.elasticsearch.index.query.QueryShardContext;
+import org.elasticsearch.index.similarity.SimilarityService;
+import org.elasticsearch.indices.IndicesModule;
+import org.elasticsearch.indices.mapper.MapperRegistry;
+import org.elasticsearch.plugins.MapperPlugin;
+import org.elasticsearch.plugins.Plugin;
+import org.elasticsearch.script.ScriptService;
+import org.elasticsearch.test.ESTestCase;
+
+import java.io.IOException;
+import java.util.Collection;
+import java.util.Map;
+
+import static java.util.Collections.emptyList;
+import static java.util.Collections.emptyMap;
+import static java.util.stream.Collectors.toList;
+import static org.mockito.Matchers.anyObject;
+import static org.mockito.Matchers.anyString;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public abstract class MapperServiceTestCase extends ESTestCase {
+
+    protected static final Settings SETTINGS = Settings.builder().put("index.version.created", Version.CURRENT).build();
+
+    protected Collection<? extends Plugin> getPlugins() {
+        return emptyList();
+    }
+
+    protected Settings getIndexSettings() {
+        return SETTINGS;
+    }
+
+    protected IndexAnalyzers createIndexAnalyzers(IndexSettings indexSettings) {
+        return new IndexAnalyzers(
+            Map.of("default", new NamedAnalyzer("default", AnalyzerScope.INDEX, new StandardAnalyzer())),
+            Map.of(),
+            Map.of()
+        );
+    }
+
+    protected final String randomIndexOptions() {
+        return randomFrom("docs", "freqs", "positions", "offsets");
+    }
+
+    protected final DocumentMapper createDocumentMapper(XContentBuilder mappings) throws IOException {
+        return createMapperService(mappings).documentMapper();
+    }
+
+    protected final MapperService createMapperService(XContentBuilder mappings) throws IOException {
+        return createMapperService(getIndexSettings(), mappings);
+    }
+
+    /**
+     * Create a {@link MapperService} like we would for an index.
+     */
+    protected final MapperService createMapperService(Settings settings, XContentBuilder mapping) throws IOException {
+        IndexMetadata meta = IndexMetadata.builder("index")
+            .settings(Settings.builder().put("index.version.created", Version.CURRENT))
+            .numberOfReplicas(0)
+            .numberOfShards(1)
+            .build();
+        IndexSettings indexSettings = new IndexSettings(meta, settings);
+        MapperRegistry mapperRegistry = new IndicesModule(
+            getPlugins().stream().filter(p -> p instanceof MapperPlugin).map(p -> (MapperPlugin) p).collect(toList())
+        ).getMapperRegistry();
+        ScriptService scriptService = new ScriptService(settings, emptyMap(), emptyMap());
+        SimilarityService similarityService = new SimilarityService(indexSettings, scriptService, Map.of());
+        MapperService mapperService = new MapperService(
+            indexSettings,
+            createIndexAnalyzers(indexSettings),
+            xContentRegistry(),
+            similarityService,
+            mapperRegistry,
+            () -> { throw new UnsupportedOperationException(); },
+            () -> true
+        );
+        merge(mapperService, mapping);
+        return mapperService;
+    }
+
+    protected final void withLuceneIndex(
+        MapperService mapperService,
+        CheckedConsumer<RandomIndexWriter, IOException> builder,
+        CheckedConsumer<IndexReader, IOException> test
+    ) throws IOException {
+        try (
+            Directory dir = newDirectory();
+            RandomIndexWriter iw = new RandomIndexWriter(random(), dir, new IndexWriterConfig(mapperService.indexAnalyzer()))
+        ) {
+            builder.accept(iw);
+            try (IndexReader reader = iw.getReader()) {
+                test.accept(reader);
+            }
+        }
+    }
+
+    protected final SourceToParse source(CheckedConsumer<XContentBuilder, IOException> build) throws IOException {
+        XContentBuilder builder = JsonXContent.contentBuilder().startObject();
+        build.accept(builder);
+        builder.endObject();
+        return new SourceToParse("test", "1", BytesReference.bytes(builder), XContentType.JSON);
+    }
+
+    /**
+     * Merge a new mapping into the one in the provided {@link MapperService}.
+     */
+    protected final void merge(MapperService mapperService, XContentBuilder mapping) throws IOException {
+        mapperService.merge(null, new CompressedXContent(BytesReference.bytes(mapping)), MapperService.MergeReason.MAPPING_UPDATE);
+    }
+
+    protected final XContentBuilder mapping(CheckedConsumer<XContentBuilder, IOException> buildFields) throws IOException {
+        XContentBuilder builder = XContentFactory.jsonBuilder().startObject().startObject("_doc").startObject("properties");
+        buildFields.accept(builder);
+        return builder.endObject().endObject().endObject();
+    }
+
+    protected final XContentBuilder fieldMapping(CheckedConsumer<XContentBuilder, IOException> buildField) throws IOException {
+        return mapping(b -> {
+            b.startObject("field");
+            buildField.accept(b);
+            b.endObject();
+        });
+    }
+
+    QueryShardContext createQueryShardContext(MapperService mapperService) {
+        QueryShardContext queryShardContext = mock(QueryShardContext.class);
+        when(queryShardContext.getMapperService()).thenReturn(mapperService);
+        when(queryShardContext.fieldMapper(anyString())).thenAnswer(inv -> mapperService.fieldType(inv.getArguments()[0].toString()));
+        when(queryShardContext.getIndexAnalyzers()).thenReturn(mapperService.getIndexAnalyzers());
+        when(queryShardContext.getSearchQuoteAnalyzer(anyObject())).thenCallRealMethod();
+        when(queryShardContext.getSearchAnalyzer(anyObject())).thenCallRealMethod();
+        when(queryShardContext.getIndexSettings()).thenReturn(mapperService.getIndexSettings());
+        when(queryShardContext.simpleMatchToIndexNames(anyObject())).thenAnswer(
+            inv -> mapperService.simpleMatchToFullName(inv.getArguments()[0].toString())
+        );
+        return queryShardContext;
+    }
+}

test/framework/src/main/java/org/elasticsearch/index/mapper/MapperTestCase.java

@@ -19,178 +19,31 @@
 
 package org.elasticsearch.index.mapper;
 
-import org.apache.lucene.analysis.standard.StandardAnalyzer;
-import org.apache.lucene.index.IndexReader;
-import org.apache.lucene.index.IndexWriterConfig;
-import org.apache.lucene.index.RandomIndexWriter;
-import org.apache.lucene.store.Directory;
-import org.elasticsearch.Version;
-import org.elasticsearch.cluster.metadata.IndexMetadata;
-import org.elasticsearch.common.CheckedConsumer;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.bytes.BytesReference;
-import org.elasticsearch.common.compress.CompressedXContent;
-import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
-import org.elasticsearch.common.xcontent.XContentFactory;
 import org.elasticsearch.common.xcontent.XContentHelper;
-import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.common.xcontent.json.JsonXContent;
-import org.elasticsearch.index.IndexSettings;
-import org.elasticsearch.index.analysis.AnalyzerScope;
-import org.elasticsearch.index.analysis.IndexAnalyzers;
-import org.elasticsearch.index.analysis.NamedAnalyzer;
-import org.elasticsearch.index.mapper.MapperService.MergeReason;
-import org.elasticsearch.index.query.QueryShardContext;
-import org.elasticsearch.index.similarity.SimilarityService;
-import org.elasticsearch.indices.IndicesModule;
-import org.elasticsearch.indices.mapper.MapperRegistry;
-import org.elasticsearch.plugins.MapperPlugin;
-import org.elasticsearch.plugins.Plugin;
-import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.search.lookup.SourceLookup;
-import org.elasticsearch.test.ESTestCase;
 
 import java.io.IOException;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
-import java.util.Map;
 import java.util.Set;
 
-import static java.util.Collections.emptyList;
-import static java.util.Collections.emptyMap;
-import static java.util.stream.Collectors.toList;
 import static org.hamcrest.Matchers.containsString;
-import static org.mockito.Matchers.anyObject;
-import static org.mockito.Matchers.anyString;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
 /**
  * Base class for testing {@link Mapper}s.
  */
-public abstract class MapperTestCase extends ESTestCase {
-    protected static final Settings SETTINGS = Settings.builder().put("index.version.created", Version.CURRENT).build();
-
-    protected Collection<? extends Plugin> getPlugins() {
-        return emptyList();
-    }
-
-    protected Settings getIndexSettings() {
-        return SETTINGS;
-    }
-
-    protected IndexAnalyzers createIndexAnalyzers(IndexSettings indexSettings) {
-        return new IndexAnalyzers(
-            Map.of("default", new NamedAnalyzer("default", AnalyzerScope.INDEX, new StandardAnalyzer())),
-            Map.of(),
-            Map.of()
-        );
-    }
-
-    protected final String randomIndexOptions() {
-        return randomFrom(new String[] { "docs", "freqs", "positions", "offsets" });
-    }
-
-    protected final DocumentMapper createDocumentMapper(XContentBuilder mappings) throws IOException {
-        return createMapperService(mappings).documentMapper();
-    }
-
-    protected final MapperService createMapperService(XContentBuilder mappings) throws IOException {
-        return createMapperService(getIndexSettings(), mappings);
-    }
-
-    /**
-     * Create a {@link MapperService} like we would for an index.
-     */
-    protected final MapperService createMapperService(Settings settings, XContentBuilder mapping) throws IOException {
-        IndexMetadata meta = IndexMetadata.builder("index")
-            .settings(Settings.builder().put("index.version.created", Version.CURRENT))
-            .numberOfReplicas(0)
-            .numberOfShards(1)
-            .build();
-        IndexSettings indexSettings = new IndexSettings(meta, Settings.EMPTY);
-        MapperRegistry mapperRegistry = new IndicesModule(
-            getPlugins().stream().filter(p -> p instanceof MapperPlugin).map(p -> (MapperPlugin) p).collect(toList())
-        ).getMapperRegistry();
-        ScriptService scriptService = new ScriptService(Settings.EMPTY, emptyMap(), emptyMap());
-        SimilarityService similarityService = new SimilarityService(indexSettings, scriptService, Map.of());
-        MapperService mapperService = new MapperService(
-            indexSettings,
-            createIndexAnalyzers(indexSettings),
-            xContentRegistry(),
-            similarityService,
-            mapperRegistry,
-            () -> { throw new UnsupportedOperationException(); },
-            () -> true
-        );
-        merge(mapperService, mapping);
-        return mapperService;
-    }
-
-    protected final void withLuceneIndex(
-        MapperService mapperService,
-        CheckedConsumer<RandomIndexWriter, IOException> builder,
-        CheckedConsumer<IndexReader, IOException> test
-    ) throws IOException {
-        try (
-            Directory dir = newDirectory();
-            RandomIndexWriter iw = new RandomIndexWriter(random(), dir, new IndexWriterConfig(mapperService.indexAnalyzer()))
-        ) {
-            builder.accept(iw);
-            try (IndexReader reader = iw.getReader()) {
-                test.accept(reader);
-            }
-        }
-    }
-
-    protected final SourceToParse source(CheckedConsumer<XContentBuilder, IOException> build) throws IOException {
-        XContentBuilder builder = JsonXContent.contentBuilder().startObject();
-        build.accept(builder);
-        builder.endObject();
-        return new SourceToParse("test", "1", BytesReference.bytes(builder), XContentType.JSON);
-    }
-
-    /**
-     * Merge a new mapping into the one in the provided {@link MapperService}.
-     */
-    protected final void merge(MapperService mapperService, XContentBuilder mapping) throws IOException {
-        mapperService.merge(null, new CompressedXContent(BytesReference.bytes(mapping)), MergeReason.MAPPING_UPDATE);
-    }
-
-    protected final XContentBuilder mapping(CheckedConsumer<XContentBuilder, IOException> buildFields) throws IOException {
-        XContentBuilder builder = XContentFactory.jsonBuilder().startObject().startObject("_doc").startObject("properties");
-        buildFields.accept(builder);
-        return builder.endObject().endObject().endObject();
-    }
-
-    protected final XContentBuilder fieldMapping(CheckedConsumer<XContentBuilder, IOException> buildField) throws IOException {
-        return mapping(b -> {
-            b.startObject("field");
-            buildField.accept(b);
-            b.endObject();
-        });
-    }
-
-    QueryShardContext createQueryShardContext(MapperService mapperService) {
-        QueryShardContext queryShardContext = mock(QueryShardContext.class);
-        when(queryShardContext.getMapperService()).thenReturn(mapperService);
-        when(queryShardContext.fieldMapper(anyString())).thenAnswer(inv -> mapperService.fieldType(inv.getArguments()[0].toString()));
-        when(queryShardContext.getIndexAnalyzers()).thenReturn(mapperService.getIndexAnalyzers());
-        when(queryShardContext.getSearchQuoteAnalyzer(anyObject())).thenCallRealMethod();
-        when(queryShardContext.getSearchAnalyzer(anyObject())).thenCallRealMethod();
-        when(queryShardContext.getIndexSettings()).thenReturn(mapperService.getIndexSettings());
-        when(queryShardContext.simpleMatchToIndexNames(anyObject())).thenAnswer(
-            inv -> mapperService.simpleMatchToFullName(inv.getArguments()[0].toString())
-        );
-        return queryShardContext;
-    }
+public abstract class MapperTestCase extends MapperServiceTestCase {
 
     protected abstract void minimalMapping(XContentBuilder b) throws IOException;
 
-    public final void testEmptyName() throws IOException {
+    public final void testEmptyName() {
         MapperParsingException e = expectThrows(MapperParsingException.class, () -> createMapperService(mapping(b -> {
             b.startObject("");
             minimalMapping(b);