Fix

server/src/main/java/org/elasticsearch/rest/action/document/RestBulkAction.java

@@ -137,10 +137,11 @@ public RestChannelConsumer prepareRequest(final RestRequest request, final NodeC
 
     static class ChunkHandler implements BaseRestHandler.RequestBodyChunkConsumer {
 
+        private final boolean allowExplicitIndex;
         private final RestRequest request;
 
-        private final BulkRequestParser.IncrementalParser parser;
         private final Supplier<IncrementalBulkService.Handler> handlerSupplier;
+        private BulkRequestParser.IncrementalParser parser;
         private IncrementalBulkService.Handler handler;
 
         private volatile RestChannel restChannel;
@@ -150,7 +151,15 @@ static class ChunkHandler implements BaseRestHandler.RequestBodyChunkConsumer {
         private final ArrayList<DocWriteRequest<?>> items = new ArrayList<>(4);
 
         ChunkHandler(boolean allowExplicitIndex, RestRequest request, Supplier<IncrementalBulkService.Handler> handlerSupplier) {
+            this.allowExplicitIndex = allowExplicitIndex;
             this.request = request;
+            this.handlerSupplier = handlerSupplier;
+        }
+
+        @Override
+        public void accept(RestChannel restChannel) {
+            this.restChannel = restChannel;
+            this.handler = handlerSupplier.get();
             this.parser = new BulkRequestParser(true, request.getRestApiVersion(), handler::loadRequestContext).incrementalParser(
                 request.param("index"),
                 request.param("routing"),
@@ -165,13 +174,6 @@ static class ChunkHandler implements BaseRestHandler.RequestBodyChunkConsumer {
                 items::add,
                 items::add
             );
-            this.handlerSupplier = handlerSupplier;
-        }
-
-        @Override
-        public void accept(RestChannel restChannel) {
-            this.restChannel = restChannel;
-            this.handler = handlerSupplier.get();
             request.contentStream().next();
         }