Addressed PR comments

Signed-off-by: Owais Kazi <owaiskazi19@gmail.com>

Author: owaiskazi19

server/src/main/java/org/opensearch/search/pipeline/SearchPipelineService.java

@@ -392,7 +392,7 @@ public PipelinedRequest resolvePipeline(SearchRequest searchRequest, IndexNameEx
             if (searchRequest.pipeline() != null) {
                 // Named pipeline specified for the request
                 pipelineId = searchRequest.pipeline();
-            } else if (state != null && searchRequest.indices() != null) {
+            } else if (state != null && searchRequest.indices() != null && searchRequest.indices().length != 0) {
                 // Check for index default pipeline
                 Index[] concreteIndices = indexNameExpressionResolver.concreteIndices(state, searchRequest);
                 for (Index index : concreteIndices) {

server/src/test/java/org/opensearch/search/pipeline/SearchPipelineServiceTests.java

@@ -115,10 +115,10 @@ private static IndexMetadata.Builder indexBuilder(String index) {
     }
 
     private static IndexMetadata.Builder indexBuilder(String index, Settings additionalSettings) {
-        return IndexMetadata.builder(index).settings(settings(additionalSettings));
+        return IndexMetadata.builder(index).settings(addAdditionalSettings(additionalSettings));
     }
 
-    private static Settings.Builder settings(Settings additionalSettings) {
+    private static Settings.Builder addAdditionalSettings(Settings additionalSettings) {
         return settings(Version.CURRENT).put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
             .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0)
             .put(additionalSettings);
@@ -1629,4 +1629,39 @@ public void testDifferentDefaultPipelineForMultipleIndices() throws Exception {
         assertEquals(5, pipelinedRequest.source().size());
     }
 
+    public void testNoIndexResolveIndexDefaultPipeline() throws Exception {
+        SearchPipelineService service = createWithProcessors();
+
+        SearchPipelineMetadata metadata = new SearchPipelineMetadata(
+            Map.of(
+                "p1",
+                new PipelineConfiguration(
+                    "p1",
+                    new BytesArray("{\"request_processors\" : [ { \"scale_request_size\": { \"scale\" : 2 } } ] }"),
+                    MediaTypeRegistry.JSON
+                )
+            )
+        );
+        Settings defaultPipelineSetting = Settings.builder()
+            .put(IndexMetadata.INDEX_NUMBER_OF_SHARDS_SETTING.getKey(), 1)
+            .put(IndexMetadata.INDEX_NUMBER_OF_REPLICAS_SETTING.getKey(), 0)
+            .put(IndexMetadata.SETTING_INDEX_VERSION_CREATED.getKey(), Version.CURRENT)
+            .put(IndexSettings.DEFAULT_SEARCH_PIPELINE.getKey(), "p1")
+            .build();
+        IndexMetadata indexMetadata = new IndexMetadata.Builder("my_index").settings(defaultPipelineSetting).build();
+        ClusterState clusterState = ClusterState.builder(new ClusterName("_name")).build();
+        ClusterState previousState = clusterState;
+        clusterState = ClusterState.builder(clusterState)
+            .metadata(Metadata.builder().put(indexMetadata, false).putCustom(SearchPipelineMetadata.TYPE, metadata))
+            .build();
+
+        ClusterChangedEvent cce = new ClusterChangedEvent("", clusterState, previousState);
+        service.applyClusterState(cce);
+
+        SearchRequest searchRequest = new SearchRequest().source(SearchSourceBuilder.searchSource().size(5));
+        PipelinedRequest pipelinedRequest = syncTransformRequest(service.resolvePipeline(searchRequest, indexNameExpressionResolver));
+        assertEquals("_none", pipelinedRequest.getPipeline().getId());
+        assertEquals(5, pipelinedRequest.source().size());
+    }
+
 }