Fix IndexOutOfBoundsException when try to map inner hits with no results returned.

Original Pull Request #1998
Closes #1997

(cherry picked from commit 2aba7a5)

Author: xhaggi

src/main/java/org/springframework/data/elasticsearch/core/SearchHitMapping.java

@@ -23,8 +23,7 @@
 import java.util.stream.Collectors;
 
 import org.elasticsearch.search.aggregations.Aggregations;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import org.springframework.data.elasticsearch.UncategorizedElasticsearchException;
 import org.springframework.data.elasticsearch.core.convert.ElasticsearchConverter;
 import org.springframework.data.elasticsearch.core.document.Document;
 import org.springframework.data.elasticsearch.core.document.NestedMetaData;
@@ -43,12 +42,11 @@
  * @author Peter-Josef Meisch
  * @author Mark Paluch
  * @author Roman Puchkovskiy
+ * @author Sascha Woo
  * @since 4.0
  */
 class SearchHitMapping<T> {
 
-	private static final Logger LOGGER = LoggerFactory.getLogger(SearchHitMapping.class);
-
 	private final Class<T> type;
 	private final ElasticsearchConverter converter;
 	private final MappingContext<? extends ElasticsearchPersistentEntity<?>, ElasticsearchPersistentProperty> mappingContext;
@@ -169,7 +167,7 @@ private Map<String, SearchHits<?>> mapInnerHits(SearchDocument searchDocument) {
 	 */
 	private SearchHits<?> mapInnerDocuments(SearchHits<SearchDocument> searchHits, Class<T> type) {
 
-		if (searchHits.getTotalHits() == 0) {
+		if (searchHits.isEmpty()) {
 			return searchHits;
 		}
 
@@ -210,7 +208,7 @@ private SearchHits<?> mapInnerDocuments(SearchHits<SearchDocument> searchHits, C
 						searchHits.getAggregations());
 			}
 		} catch (Exception e) {
-			LOGGER.warn("Could not map inner_hits", e);
+			throw new UncategorizedElasticsearchException("Unable to convert inner hits.", e);
 		}
 
 		return searchHits;

src/test/java/org/springframework/data/elasticsearch/core/ElasticsearchTemplateTests.java

@@ -53,6 +53,10 @@
 import org.elasticsearch.action.update.UpdateRequest;
 import org.elasticsearch.cluster.metadata.AliasMetadata;
 import org.elasticsearch.index.VersionType;
+import org.elasticsearch.index.query.InnerHitBuilder;
+import org.elasticsearch.index.query.QueryBuilders;
+import org.elasticsearch.join.query.HasChildQueryBuilder;
+import org.elasticsearch.join.query.JoinQueryBuilders;
 import org.elasticsearch.join.query.ParentIdQueryBuilder;
 import org.elasticsearch.script.Script;
 import org.elasticsearch.script.ScriptType;
@@ -2988,6 +2992,46 @@ public void shouldAddAliasWithGivenRoutingValue() {
 		indexOperations.removeAlias(aliasQuery);
 	}
 
+	@Test // #1997
+	@DisplayName("should return document with inner hits size zero")
+	void shouldReturnDocumentWithInnerHitsSizeZero() {
+
+		// given
+		SampleJoinEntity sampleQuestionEntity1 = new SampleJoinEntity();
+		sampleQuestionEntity1.setUuid("q1");
+		sampleQuestionEntity1.setText("This is a question");
+		sampleQuestionEntity1.setMyJoinField(new JoinField<>("question"));
+
+		SampleJoinEntity sampleAnswerEntity1 = new SampleJoinEntity();
+		sampleAnswerEntity1.setUuid("a1");
+		sampleAnswerEntity1.setText("This is an answer");
+		sampleAnswerEntity1.setMyJoinField(new JoinField<>("answer", sampleQuestionEntity1.getUuid()));
+
+		SampleJoinEntity sampleAnswerEntity2 = new SampleJoinEntity();
+		sampleAnswerEntity1.setUuid("a2");
+		sampleAnswerEntity1.setText("This is an answer");
+		sampleAnswerEntity1.setMyJoinField(new JoinField<>("answer", sampleQuestionEntity1.getUuid()));
+
+		IndexOperations indexOps = operations.indexOps(SampleJoinEntity.class);
+		operations.save(Arrays.asList(sampleQuestionEntity1, sampleAnswerEntity1, sampleAnswerEntity2));
+		indexOps.refresh();
+
+		// when
+		Query query = new NativeSearchQueryBuilder().withQuery(
+				JoinQueryBuilders.hasChildQuery("answer", matchAllQuery(), org.apache.lucene.search.join.ScoreMode.Avg)
+						.innerHit(new InnerHitBuilder("innerHits").setSize(0)))
+				.build();
+
+		SearchHits<SampleJoinEntity> searchHits = operations.search(query, SampleJoinEntity.class);
+
+		// then
+		assertThat(searchHits).isNotNull();
+		assertThat(searchHits.getTotalHits()).isEqualTo(1);
+		assertThat(searchHits.getSearchHits()).hasSize(1);
+		assertThat(searchHits.getSearchHit(0).getInnerHits().size()).isEqualTo(1);
+		assertThat(searchHits.getSearchHit(0).getInnerHits("innerHits").getTotalHits()).isEqualTo(1);
+	}
+
 	@Test // DATAES-541
 	public void shouldRemoveAlias() {