Bug fix: Fix NPE when parsing field names in query parser.

.gitignore

@@ -20,6 +20,8 @@ gradle-app.setting
 # JDT-specific (Eclipse Java Development Tools)
 .classpath
 
+# Intellij files
+.idea/
 
 # Compiled class file
 *.class
@@ -86,4 +88,4 @@ Icon
 .AppleDesktop
 Network Trash Folder
 Temporary Items
-.apdisk
+.apdisk

src/main/java/org/opensearch/search/relevance/actionfilter/SearchActionFilter.java

@@ -251,8 +251,8 @@ public void onResponse(final Response response) {
           logger.info("Re-ranking overhead time: {}ms",
               tookInMillis - searchResponse.getTook().getMillis());
         } catch (final Exception e) {
-          logger.error("Failed to parse search response.", e);
-          throw new OpenSearchException("Failed to parse a search response.", e);
+          logger.error("Result transformer operations failed.", e);
+          throw new OpenSearchException("Result transformer operations failed.", e);
         }
       }
 

src/main/java/org/opensearch/search/relevance/transformer/kendraintelligentranking/preprocess/QueryParser.java

@@ -22,15 +22,25 @@
 public class QueryParser {
   private static final Logger logger = LogManager.getLogger(QueryParser.class);
 
+  private static final String BODY_FIELD_REQUIRED_ERROR_MESSAGE =
+      "Property [" + BODY_FIELD + "] must be specified";
   private static final String FILED_MISMATCH_ERROR_MESSAGE =
       "Mismatch: Field configured in %s property [%s] is not present in query fields [%s]. Will not apply Kendra Intelligent Ranking.";
+  private static final String QUERY_PARSER_RESULT_LOG =
+      "Kendra Intelligent Ranker query parser fields for query type [%s]: bodyField: %s, titleField: %s";
+  private static final String QUERY_PARSER_RESULT_LOG_WITHOUT_TITLE =
+      "Kendra Intelligent Ranker query parser fields for query type [%s]: bodyField: %s";
 
   public QueryParserResult parse(
       final QueryBuilder query,
       final List<String> bodyFieldSetting,
       final List<String> titleFieldSetting) {
-    final String bodyFieldFromSetting = bodyFieldSetting.isEmpty() ? null : bodyFieldSetting.get(0);
-    final String titleFieldFromSetting = titleFieldSetting.isEmpty() ? null : titleFieldSetting.get(0);
+    if (bodyFieldSetting == null || bodyFieldSetting.isEmpty()) {
+      throw new IllegalArgumentException(BODY_FIELD_REQUIRED_ERROR_MESSAGE);
+    }
+
+    final String bodyFieldFromSetting = bodyFieldSetting.get(0);
+    final String titleFieldFromSetting = (titleFieldSetting == null || titleFieldSetting.isEmpty()) ? null : titleFieldSetting.get(0);
     QueryParserResult result = null;
 
     if (query instanceof MatchQueryBuilder) {
@@ -51,6 +61,8 @@ private QueryParserResult parseMatchQuery(MatchQueryBuilder matchQuery, String b
           bodyFieldFromSetting, matchQuery.fieldName()));
     } else {
       result = new QueryParserResult(matchQuery.value().toString(), bodyFieldFromSetting);
+      logger.info(String.format(Locale.ENGLISH, QUERY_PARSER_RESULT_LOG_WITHOUT_TITLE,
+          matchQuery.NAME, result.bodyFieldName));
     }
     return result;
   }
@@ -76,6 +88,8 @@ private QueryParserResult parseMultiMatchQuery(MultiMatchQueryBuilder multiMatch
     } else {
       final String titleFieldToUse = configuredTitleFieldPresentInQuery ? titleFieldFromSetting : null;
       result = new QueryParserResult(multiMatchQuery.value().toString(), bodyFieldFromSetting, titleFieldToUse);
+      logger.info(String.format(Locale.ENGLISH, QUERY_PARSER_RESULT_LOG,
+          multiMatchQuery.NAME, result.bodyFieldName, result.titleFieldName));
     }
     return result;
   }

src/test/java/org/opensearch/search/relevance/transformer/kendraintelligentranking/preprocess/QueryParserTests.java

@@ -24,6 +24,14 @@ public class QueryParserTests extends OpenSearchTestCase {
   private static final String INVALID_FIELD = "invalidField";
   private QueryParser queryParser = new QueryParser();
 
+  public void testParse_BodyFieldNull_ThrowsException() {
+    assertThrows(IllegalArgumentException.class, () -> queryParser.parse(
+        new MatchQueryBuilder(TEST_BODY_FIELD, TEST_QUERY_TEXT),
+        null,
+        null)
+    );
+  }
+
   public void testParse_Match_RequestFieldMatchesSetting() {
     QueryParser.QueryParserResult queryParserResult = queryParser.parse(
         new MatchQueryBuilder(TEST_BODY_FIELD, TEST_QUERY_TEXT),
@@ -33,6 +41,15 @@ public void testParse_Match_RequestFieldMatchesSetting() {
     performQueryParserResultAssertions(queryParserResult, TEST_QUERY_TEXT, TEST_BODY_FIELD, null);
   }
 
+  public void testParse_Match_TitleFieldSettingNull() {
+    QueryParser.QueryParserResult queryParserResult = queryParser.parse(
+        new MatchQueryBuilder(TEST_BODY_FIELD, TEST_QUERY_TEXT),
+        Arrays.asList(TEST_BODY_FIELD),
+        null);
+
+    performQueryParserResultAssertions(queryParserResult, TEST_QUERY_TEXT, TEST_BODY_FIELD, null);
+  }
+
   public void testParse_Match_RequestFieldDoesNotMatchSetting() {
     QueryParser.QueryParserResult queryParserResult = queryParser.parse(
         new MatchQueryBuilder(TEST_BODY_FIELD, TEST_QUERY_TEXT),
@@ -60,6 +77,15 @@ public void testParse_MultiMatch_OnlyBodyFieldMatchesSetting() {
     performQueryParserResultAssertions(queryParserResult, TEST_QUERY_TEXT, TEST_BODY_FIELD, null);
   }
 
+  public void testParse_MultiMatch_TitleFieldSettingNull() {
+    QueryParser.QueryParserResult queryParserResult = queryParser.parse(
+        new MultiMatchQueryBuilder(TEST_QUERY_TEXT, TEST_BODY_FIELD, TEST_TITLE_FIELD),
+        Arrays.asList(TEST_BODY_FIELD),
+        null);
+
+    performQueryParserResultAssertions(queryParserResult, TEST_QUERY_TEXT, TEST_BODY_FIELD, null);
+  }
+
   public void testParse_MultiMatch_RequestFieldMatchesSetting_WithFieldBoosting() {
     MultiMatchQueryBuilder multiMatchQueryBuilder = new MultiMatchQueryBuilder(TEST_QUERY_TEXT, TEST_TITLE_FIELD, TEST_BODY_FIELD);
     multiMatchQueryBuilder.field(TEST_BODY_FIELD, 1.5f);