Set maxScore for empty TopDocs to Nan rather than 0 (#32938)

We used to set `maxScore` to `0` within `TopDocs` in situations where there is really no score as the size was set to `0` and scores were not even tracked. In such scenarios, `Float.Nan` is more appropriate, which gets converted to `max_score: null` on the REST layer. That's also more consistent with lucene which set `maxScore` to `Float.Nan` when merging empty `TopDocs` (see `TopDocs#merge`).

client/rest-high-level/src/test/java/org/elasticsearch/client/SearchIT.java

@@ -256,7 +256,7 @@ public class SearchIT extends ESRestHighLevelClientTestCase {
         assertNull(searchResponse.getSuggest());
         assertEquals(Collections.emptyMap(), searchResponse.getProfileResults());
         assertEquals(0, searchResponse.getHits().getHits().length);
-        assertEquals(0f, searchResponse.getHits().getMaxScore(), 0f);
+        assertEquals(Float.NaN, searchResponse.getHits().getMaxScore(), 0f);
         Terms termsAgg = searchResponse.getAggregations().get("agg1");
         assertEquals("agg1", termsAgg.getName());
         assertEquals(2, termsAgg.getBuckets().size());
@@ -293,7 +293,7 @@ public class SearchIT extends ESRestHighLevelClientTestCase {
         assertEquals(Collections.emptyMap(), searchResponse.getProfileResults());
         assertEquals(5, searchResponse.getHits().totalHits);
         assertEquals(0, searchResponse.getHits().getHits().length);
-        assertEquals(0f, searchResponse.getHits().getMaxScore(), 0f);
+        assertEquals(Float.NaN, searchResponse.getHits().getMaxScore(), 0f);
         Range rangeAgg = searchResponse.getAggregations().get("agg1");
         assertEquals("agg1", rangeAgg.getName());
         assertEquals(2, rangeAgg.getBuckets().size());
@@ -323,7 +323,7 @@ public class SearchIT extends ESRestHighLevelClientTestCase {
         assertNull(searchResponse.getSuggest());
         assertEquals(Collections.emptyMap(), searchResponse.getProfileResults());
         assertEquals(0, searchResponse.getHits().getHits().length);
-        assertEquals(0f, searchResponse.getHits().getMaxScore(), 0f);
+        assertEquals(Float.NaN, searchResponse.getHits().getMaxScore(), 0f);
         Terms termsAgg = searchResponse.getAggregations().get("agg1");
         assertEquals("agg1", termsAgg.getName());
         assertEquals(2, termsAgg.getBuckets().size());
@@ -375,7 +375,7 @@ public class SearchIT extends ESRestHighLevelClientTestCase {
         assertEquals(Collections.emptyMap(), searchResponse.getProfileResults());
         assertEquals(5, searchResponse.getHits().totalHits);
         assertEquals(0, searchResponse.getHits().getHits().length);
-        assertEquals(0f, searchResponse.getHits().getMaxScore(), 0f);
+        assertEquals(Float.NaN, searchResponse.getHits().getMaxScore(), 0f);
         assertEquals(1, searchResponse.getAggregations().asList().size());
         MatrixStats matrixStats = searchResponse.getAggregations().get("agg1");
         assertEquals(5, matrixStats.getFieldCount("num"));
@@ -474,7 +474,7 @@ public class SearchIT extends ESRestHighLevelClientTestCase {
         assertEquals(Collections.emptyMap(), searchResponse.getProfileResults());
         assertEquals(3, searchResponse.getHits().totalHits);
         assertEquals(0, searchResponse.getHits().getHits().length);
-        assertEquals(0f, searchResponse.getHits().getMaxScore(), 0f);
+        assertEquals(Float.NaN, searchResponse.getHits().getMaxScore(), 0f);
         assertEquals(1, searchResponse.getAggregations().asList().size());
         Terms terms = searchResponse.getAggregations().get("top-tags");
         assertEquals(0, terms.getDocCountError());
@@ -513,7 +513,7 @@ public class SearchIT extends ESRestHighLevelClientTestCase {
         assertNull(searchResponse.getAggregations());
         assertEquals(Collections.emptyMap(), searchResponse.getProfileResults());
         assertEquals(0, searchResponse.getHits().totalHits);
-        assertEquals(0f, searchResponse.getHits().getMaxScore(), 0f);
+        assertEquals(Float.NaN, searchResponse.getHits().getMaxScore(), 0f);
         assertEquals(0, searchResponse.getHits().getHits().length);
         assertEquals(1, searchResponse.getSuggest().size());
 

docs/reference/aggregations/bucket/children-aggregation.asciidoc

@@ -144,7 +144,7 @@ Possible response:
   },
   "hits": {
     "total": 3,
-    "max_score": 0.0,
+    "max_score": null,
     "hits": []
   },
   "aggregations": {

docs/reference/getting-started.asciidoc

@@ -1141,7 +1141,7 @@ And the response (partially shown):
   },
   "hits" : {
     "total" : 1000,
-    "max_score" : 0.0,
+    "max_score" : null,
     "hits" : [ ]
   },
   "aggregations" : {

docs/reference/mapping/params/normalizer.asciidoc

@@ -151,7 +151,7 @@ returns
   },
   "hits": {
     "total": 3,
-    "max_score": 0.0,
+    "max_score": null,
     "hits": []
   },
   "aggregations": {

docs/reference/migration/migrate_7_0/search.asciidoc

@@ -100,3 +100,8 @@ and the context is only accepted if `path` points to a field with `geo_point` ty
 `max_concurrent_shard_requests` used to limit the total number of concurrent shard
 requests a single high level search request can execute. In 7.0 this changed to be the
 max number of concurrent shard requests per node. The default is now `5`.
+
+==== `max_score` set to `null` when scores are not tracked
+
+`max_score` used to be set to `0` whenever scores are not tracked. `null` is now used
+instead which is a more appropriate value for a scenario where scores are not available.

docs/reference/search/request-body.asciidoc

@@ -161,7 +161,7 @@ be set to `true` in the response.
   },
   "hits": {
     "total": 1,
-    "max_score": 0.0,
+    "max_score": null,
     "hits": []
   }
 }

docs/reference/search/suggesters/completion-suggest.asciidoc

@@ -258,7 +258,7 @@ Which should look like:
     },
     "hits": {
         "total" : 0,
-        "max_score" : 0.0,
+        "max_score" : null,
         "hits" : []
     },
     "suggest": {

modules/parent-join/src/main/java/org/elasticsearch/join/query/ParentChildInnerHitContextBuilder.java

@@ -131,7 +131,7 @@ class ParentChildInnerHitContextBuilder extends InnerHitContextBuilder {
                     for (LeafReaderContext ctx : context.searcher().getIndexReader().leaves()) {
                         intersect(weight, innerHitQueryWeight, totalHitCountCollector, ctx);
                     }
-                    result[i] = new TopDocs(totalHitCountCollector.getTotalHits(), Lucene.EMPTY_SCORE_DOCS, 0);
+                    result[i] = new TopDocs(totalHitCountCollector.getTotalHits(), Lucene.EMPTY_SCORE_DOCS, Float.NaN);
                 } else {
                     int topN = Math.min(from() + size(), context.searcher().getIndexReader().maxDoc());
                     TopDocsCollector<?> topDocsCollector;

rest-api-spec/src/main/resources/rest-api-spec/test/scroll/10_basic.yml

@@ -233,3 +233,51 @@
           query:
             match_all: {}
           size: 0
+
+---
+"Scroll max_score is null":
+  - skip:
+      version: " - 6.99.99"
+      reason:  max_score was set to 0 rather than null before 7.0
+
+  - do:
+      indices.create:
+        index: test_scroll
+  - do:
+      index:
+        index:  test_scroll
+        type:   test
+        id:     42
+        body:   { foo: 1 }
+
+  - do:
+      index:
+        index:  test_scroll
+        type:   test
+        id:     43
+        body:   { foo: 2 }
+
+  - do:
+      indices.refresh: {}
+
+  - do:
+      search:
+        index: test_scroll
+        size: 1
+        scroll: 1m
+        sort: foo
+        body:
+          query:
+            match_all: {}
+
+  - set: {_scroll_id: scroll_id}
+  - length: {hits.hits:      1    }
+  - match: { hits.max_score: null }
+
+  - do:
+      scroll:
+        scroll_id: $scroll_id
+        scroll: 1m
+
+  - length: {hits.hits:      1    }
+  - match: { hits.max_score: null }

rest-api-spec/src/main/resources/rest-api-spec/test/search/110_field_collapsing.yml

@@ -244,6 +244,23 @@ setup:
   - match: { hits.total: 6 }
   - length: { hits.hits: 0 }
 
+---
+"no hits and inner_hits max_score null":
+
+  - skip:
+      version: " - 6.99.99"
+      reason:  max_score was set to 0 rather than null before 7.0
+
+  - do:
+      search:
+        index: test
+        body:
+          size: 0
+          collapse: { field: numeric_group, inner_hits: { name: sub_hits, size: 1} }
+          sort: [{ sort: desc }]
+
+  - match: { hits.max_score: null }
+
 ---
 "field collapsing and multiple inner_hits":
 

rest-api-spec/src/main/resources/rest-api-spec/test/search/140_pre_filter_search_shards.yml

@@ -128,7 +128,6 @@ setup:
   - match: { hits.total: 2 }
   - match: { aggregations.some_agg.doc_count: 3 }
 
-
   - do:
       search:
         pre_filter_shard_size: 1

rest-api-spec/src/main/resources/rest-api-spec/test/search/190_index_prefix_search.yml

@@ -39,6 +39,7 @@ setup:
         df: text
 
   - match: {hits.total: 1}
+  - match: {hits.max_score: 1}
   - match: {hits.hits.0._score: 1}
 
   - do:
@@ -52,6 +53,7 @@ setup:
               boost: 2
 
   - match: {hits.total: 1}
+  - match: {hits.max_score: 2}
   - match: {hits.hits.0._score: 2}
 
   - do:
@@ -61,6 +63,7 @@ setup:
         df: text
 
   - match: {hits.total: 1}
+  - match: {hits.max_score: 1}
   - match: {hits.hits.0._score: 1}
 
 ---

rest-api-spec/src/main/resources/rest-api-spec/test/search/210_rescore_explain.yml

@@ -29,6 +29,7 @@
               query_weight: 5
               rescore_query_weight: 10
 
+  - match: {hits.max_score: 15}
   - match: { hits.hits.0._score: 15 }
   - match: { hits.hits.0._explanation.value: 15 }
 

server/src/main/java/org/elasticsearch/common/lucene/Lucene.java

@@ -101,7 +101,7 @@ public class Lucene {
 
     public static final ScoreDoc[] EMPTY_SCORE_DOCS = new ScoreDoc[0];
 
-    public static final TopDocs EMPTY_TOP_DOCS = new TopDocs(0, EMPTY_SCORE_DOCS, 0.0f);
+    public static final TopDocs EMPTY_TOP_DOCS = new TopDocs(0, EMPTY_SCORE_DOCS, Float.NaN);
 
     public static Version parseVersion(@Nullable String version, Version defaultVersion, Logger logger) {
         if (version == null) {

server/src/main/java/org/elasticsearch/index/query/NestedQueryBuilder.java

@@ -398,7 +398,7 @@ public class NestedQueryBuilder extends AbstractQueryBuilder<NestedQueryBuilder>
                 if (size() == 0) {
                     TotalHitCountCollector totalHitCountCollector = new TotalHitCountCollector();
                     intersect(weight, innerHitQueryWeight, totalHitCountCollector, ctx);
-                    result[i] = new TopDocs(totalHitCountCollector.getTotalHits(), Lucene.EMPTY_SCORE_DOCS, 0);
+                    result[i] = new TopDocs(totalHitCountCollector.getTotalHits(), Lucene.EMPTY_SCORE_DOCS, Float.NaN);
                 } else {
                     int topN = Math.min(from() + size(), context.searcher().getIndexReader().maxDoc());
                     TopDocsCollector<?> topDocsCollector;

server/src/main/java/org/elasticsearch/search/query/QueryPhase.java

@@ -95,7 +95,7 @@ public class QueryPhase implements SearchPhase {
             suggestPhase.execute(searchContext);
             // TODO: fix this once we can fetch docs for suggestions
             searchContext.queryResult().topDocs(
-                    new TopDocs(0, Lucene.EMPTY_SCORE_DOCS, 0),
+                    new TopDocs(0, Lucene.EMPTY_SCORE_DOCS, Float.NaN),
                     new DocValueFormat[0]);
             return;
         }

server/src/main/java/org/elasticsearch/search/query/TopDocsCollectorContext.java

@@ -120,7 +120,7 @@ abstract class TopDocsCollectorContext extends QueryCollectorContext {
         @Override
         void postProcess(QuerySearchResult result) {
             final int totalHitCount = hitCountSupplier.getAsInt();
-            result.topDocs(new TopDocs(totalHitCount, Lucene.EMPTY_SCORE_DOCS, 0), null);
+            result.topDocs(new TopDocs(totalHitCount, Lucene.EMPTY_SCORE_DOCS, Float.NaN), null);
         }
     }
 

server/src/test/java/org/elasticsearch/search/aggregations/metrics/TopHitsIT.java

@@ -321,7 +321,7 @@ public class TopHitsIT extends ESIntegTestCase {
 
         assertThat(response.getHits().getTotalHits(), equalTo(8L));
         assertThat(response.getHits().getHits().length, equalTo(0));
-        assertThat(response.getHits().getMaxScore(), equalTo(0f));
+        assertThat(response.getHits().getMaxScore(), equalTo(Float.NaN));
         Terms terms = response.getAggregations().get("terms");
         assertThat(terms, notNullValue());
         assertThat(terms.getName(), equalTo("terms"));
@@ -356,7 +356,7 @@ public class TopHitsIT extends ESIntegTestCase {
 
         assertThat(response.getHits().getTotalHits(), equalTo(8L));
         assertThat(response.getHits().getHits().length, equalTo(0));
-        assertThat(response.getHits().getMaxScore(), equalTo(0f));
+        assertThat(response.getHits().getMaxScore(), equalTo(Float.NaN));
         terms = response.getAggregations().get("terms");
         assertThat(terms, notNullValue());
         assertThat(terms.getName(), equalTo("terms"));

server/src/test/java/org/elasticsearch/search/query/QueryPhaseTests.java

@@ -67,6 +67,7 @@ import java.util.List;
 
 import static org.hamcrest.Matchers.anyOf;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.greaterThan;
 import static org.hamcrest.Matchers.greaterThanOrEqualTo;
 import static org.hamcrest.Matchers.instanceOf;
 
@@ -103,6 +104,7 @@ public class QueryPhaseTests extends IndexShardTestCase {
         final boolean rescore = QueryPhase.execute(context, searcher, checkCancelled -> {});
         assertFalse(rescore);
         assertEquals(searcher.count(query), context.queryResult().topDocs().totalHits);
+        assertThat(context.queryResult().topDocs().getMaxScore(), equalTo(Float.NaN));
     }
 
     private void countTestCase(boolean withDeletions) throws Exception {
@@ -172,11 +174,14 @@ public class QueryPhaseTests extends IndexShardTestCase {
 
         QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
         assertEquals(1, context.queryResult().topDocs().totalHits);
+        assertThat(context.queryResult().topDocs().scoreDocs.length, equalTo(0));
+        assertThat(context.queryResult().topDocs().getMaxScore(), equalTo(Float.NaN));
 
         contextSearcher = new IndexSearcher(reader);
         context.parsedPostFilter(new ParsedQuery(new MatchNoDocsQuery()));
         QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
         assertEquals(0, context.queryResult().topDocs().totalHits);
+        assertThat(context.queryResult().topDocs().getMaxScore(), equalTo(Float.NaN));
         reader.close();
         dir.close();
     }
@@ -205,13 +210,13 @@ public class QueryPhaseTests extends IndexShardTestCase {
             context.parsedPostFilter(new ParsedQuery(new TermQuery(new Term("foo", Integer.toString(i)))));
             QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
             assertEquals(1, context.queryResult().topDocs().totalHits);
+            assertThat(context.queryResult().topDocs().getMaxScore(), equalTo(1F));
             assertThat(context.queryResult().topDocs().scoreDocs.length, equalTo(1));
         }
         reader.close();
         dir.close();
     }
 
-
     public void testMinScoreDisablesCountOptimization() throws Exception {
         Directory dir = newDirectory();
         final Sort sort = new Sort(new SortField("rank", SortField.Type.INT));
@@ -230,11 +235,13 @@ public class QueryPhaseTests extends IndexShardTestCase {
         context.setTask(new SearchTask(123L, "", "", "", null, Collections.emptyMap()));
         QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
         assertEquals(1, context.queryResult().topDocs().totalHits);
+        assertThat(context.queryResult().topDocs().getMaxScore(), equalTo(Float.NaN));
 
         contextSearcher = new IndexSearcher(reader);
         context.minimumScore(100);
         QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
         assertEquals(0, context.queryResult().topDocs().totalHits);
+        assertThat(context.queryResult().topDocs().getMaxScore(), equalTo(Float.NaN));
         reader.close();
         dir.close();
     }
@@ -289,6 +296,7 @@ public class QueryPhaseTests extends IndexShardTestCase {
 
         QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
         assertThat(context.queryResult().topDocs().totalHits, equalTo((long) numDocs));
+        assertThat(context.queryResult().topDocs().getMaxScore(), equalTo(1F));
         assertNull(context.queryResult().terminatedEarly());
         assertThat(context.terminateAfter(), equalTo(0));
         assertThat(context.queryResult().getTotalHits(), equalTo((long) numDocs));
@@ -296,9 +304,11 @@ public class QueryPhaseTests extends IndexShardTestCase {
         contextSearcher = getAssertingEarlyTerminationSearcher(reader, size);
         QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
         assertThat(context.queryResult().topDocs().totalHits, equalTo((long) numDocs));
+        assertThat(context.queryResult().topDocs().getMaxScore(), equalTo(1F));
         assertTrue(context.queryResult().terminatedEarly());
         assertThat(context.terminateAfter(), equalTo(size));
         assertThat(context.queryResult().getTotalHits(), equalTo((long) numDocs));
+        assertThat(context.queryResult().topDocs().getMaxScore(), equalTo(1F));
         assertThat(context.queryResult().topDocs().scoreDocs[0].doc, greaterThanOrEqualTo(size));
         reader.close();
         dir.close();
@@ -334,12 +344,14 @@ public class QueryPhaseTests extends IndexShardTestCase {
             QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
             assertTrue(context.queryResult().terminatedEarly());
             assertThat(context.queryResult().topDocs().totalHits, equalTo(1L));
+            assertThat(context.queryResult().topDocs().getMaxScore(), equalTo(1F));
             assertThat(context.queryResult().topDocs().scoreDocs.length, equalTo(1));
 
             context.setSize(0);
             QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
             assertTrue(context.queryResult().terminatedEarly());
             assertThat(context.queryResult().topDocs().totalHits, equalTo(1L));
+            assertThat(context.queryResult().topDocs().getMaxScore(), equalTo(Float.NaN));
             assertThat(context.queryResult().topDocs().scoreDocs.length, equalTo(0));
         }
 
@@ -348,6 +360,7 @@ public class QueryPhaseTests extends IndexShardTestCase {
             QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
             assertTrue(context.queryResult().terminatedEarly());
             assertThat(context.queryResult().topDocs().totalHits, equalTo(1L));
+            assertThat(context.queryResult().topDocs().getMaxScore(), equalTo(1F));
             assertThat(context.queryResult().topDocs().scoreDocs.length, equalTo(1));
         }
         {
@@ -360,6 +373,7 @@ public class QueryPhaseTests extends IndexShardTestCase {
             QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
             assertTrue(context.queryResult().terminatedEarly());
             assertThat(context.queryResult().topDocs().totalHits, equalTo(1L));
+            assertThat(context.queryResult().topDocs().getMaxScore(), greaterThan(0f));
             assertThat(context.queryResult().topDocs().scoreDocs.length, equalTo(1));
 
             context.setSize(0);
@@ -367,6 +381,7 @@ public class QueryPhaseTests extends IndexShardTestCase {
             QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
             assertTrue(context.queryResult().terminatedEarly());
             assertThat(context.queryResult().topDocs().totalHits, equalTo(1L));
+            assertThat(context.queryResult().topDocs().getMaxScore(), equalTo(Float.NaN));
             assertThat(context.queryResult().topDocs().scoreDocs.length, equalTo(0));
         }
         {
@@ -376,6 +391,7 @@ public class QueryPhaseTests extends IndexShardTestCase {
             QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
             assertTrue(context.queryResult().terminatedEarly());
             assertThat(context.queryResult().topDocs().totalHits, equalTo(1L));
+            assertThat(context.queryResult().topDocs().getMaxScore(), greaterThan(0f));
             assertThat(context.queryResult().topDocs().scoreDocs.length, equalTo(1));
             assertThat(collector.getTotalHits(), equalTo(1));
             context.queryCollectors().clear();
@@ -387,6 +403,7 @@ public class QueryPhaseTests extends IndexShardTestCase {
             QueryPhase.execute(context, contextSearcher, checkCancelled -> {});
             assertTrue(context.queryResult().terminatedEarly());
             assertThat(context.queryResult().topDocs().totalHits, equalTo(1L));
+            assertThat(context.queryResult().topDocs().getMaxScore(), equalTo(Float.NaN));
             assertThat(context.queryResult().topDocs().scoreDocs.length, equalTo(0));
             assertThat(collector.getTotalHits(), equalTo(1));
         }
@@ -539,19 +556,19 @@ public class QueryPhaseTests extends IndexShardTestCase {
         dir.close();
     }
 
-    static IndexSearcher getAssertingEarlyTerminationSearcher(IndexReader reader, int size) {
+    private static IndexSearcher getAssertingEarlyTerminationSearcher(IndexReader reader, int size) {
         return new IndexSearcher(reader) {
             protected void search(List<LeafReaderContext> leaves, Weight weight, Collector collector) throws IOException {
-                final Collector in = new AssertingEalyTerminationFilterCollector(collector, size);
+                final Collector in = new AssertingEarlyTerminationFilterCollector(collector, size);
                 super.search(leaves, weight, in);
             }
         };
     }
 
-    private static class AssertingEalyTerminationFilterCollector extends FilterCollector {
+    private static class AssertingEarlyTerminationFilterCollector extends FilterCollector {
         private final int size;
 
-        AssertingEalyTerminationFilterCollector(Collector in, int size) {
+        AssertingEarlyTerminationFilterCollector(Collector in, int size) {
             super(in);
             this.size = size;
         }

test/framework/src/main/java/org/elasticsearch/test/rest/yaml/section/MatchAssertion.java

@@ -32,6 +32,7 @@ import static org.elasticsearch.test.hamcrest.RegexMatcher.matches;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.instanceOf;
 import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertThat;
 
 /**
@@ -70,8 +71,13 @@ public class MatchAssertion extends Assertion {
             }
         }
 
-        assertNotNull("field [" + getField() + "] is null", actualValue);
         logger.trace("assert that [{}] matches [{}] (field [{}])", actualValue, expectedValue, getField());
+        if (expectedValue == null) {
+            assertNull("field [" + getField() + "] should be null but was [" + actualValue + "]", actualValue);
+            return;
+        }
+        assertNotNull("field [" + getField() + "] is null", actualValue);
+
         if (actualValue.getClass().equals(safeClass(expectedValue)) == false) {
             if (actualValue instanceof Number && expectedValue instanceof Number) {
                 //Double 1.0 is equal to Integer 1

test/framework/src/test/java/org/elasticsearch/test/rest/yaml/section/MatchAssertionTests.java

@@ -0,0 +1,42 @@
+/*
+ * 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.test.rest.yaml.section;
+
+import org.elasticsearch.common.xcontent.XContentLocation;
+import org.elasticsearch.test.ESTestCase;
+
+public class MatchAssertionTests extends ESTestCase  {
+
+    public void testNull() {
+        XContentLocation xContentLocation = new XContentLocation(0, 0);
+        {
+            MatchAssertion matchAssertion = new MatchAssertion(xContentLocation, "field", null);
+            matchAssertion.doAssert(null, null);
+            expectThrows(AssertionError.class, () -> matchAssertion.doAssert("non-null", null));
+        }
+        {
+            MatchAssertion matchAssertion = new MatchAssertion(xContentLocation, "field", "non-null");
+            expectThrows(AssertionError.class, () -> matchAssertion.doAssert(null, "non-null"));
+        }
+        {
+            MatchAssertion matchAssertion = new MatchAssertion(xContentLocation, "field", "/exp/");
+            expectThrows(AssertionError.class, () -> matchAssertion.doAssert(null, "/exp/"));
+        }
+    }
+}