Reverting to old changes for indices map

Signed-off-by: Sagar Upadhyaya <sagar.upadhyaya.121@gmail.com>

server/src/main/java/org/opensearch/indices/IndicesService.java

@@ -178,7 +178,6 @@
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
-import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -194,6 +193,7 @@
 import java.util.stream.Collectors;
 
 import static java.util.Collections.emptyList;
+import static java.util.Collections.emptyMap;
 import static java.util.Collections.unmodifiableMap;
 import static org.opensearch.common.collect.MapBuilder.newMapBuilder;
 import static org.opensearch.common.util.concurrent.OpenSearchExecutors.daemonThreadFactory;
@@ -333,7 +333,7 @@ public class IndicesService extends AbstractLifecycleComponent
     private final ScriptService scriptService;
     private final ClusterService clusterService;
     private final Client client;
-    private Map<String, IndexService> indices = new ConcurrentHashMap<>();
+    private volatile Map<String, IndexService> indices = emptyMap();
     private final Map<Index, List<PendingDelete>> pendingDeletes = new HashMap<>();
     private final AtomicInteger numUncompletedDeletes = new AtomicInteger();
     private final OldShardsStats oldShardsStats = new OldShardsStats();