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

Author: xhaggi

Diff for: src/main/java/org/springframework/data/elasticsearch/core/SearchHitMapping.java

@@ -45,6 +45,7 @@
  * @author Mark Paluch
  * @author Roman Puchkovskiy
  * @author Matt Gilene
+ * @author Sascha Woo
  * @since 4.0
  */
 public class SearchHitMapping<T> {
@@ -194,7 +195,7 @@ private Map<String, SearchHits<?>> mapInnerHits(SearchDocument searchDocument) {
 	 */
 	private SearchHits<?> mapInnerDocuments(SearchHits<SearchDocument> searchHits, Class<T> type) {
 
-		if (searchHits.getTotalHits() == 0) {
+		if (searchHits == null || searchHits.isEmpty()) {
 			return searchHits;
 		}