From 75d4a4def4ce86f160db2d6fd59266029e3a6756 Mon Sep 17 00:00:00 2001
From: Armin Braun <me@obrown.io>
Date: Mon, 4 May 2020 19:38:21 +0200
Subject: [PATCH] Fix potential NPEin Netty4Transport.stopInternal (#56080)
 (#56129)

Closes #56068
---
 .../transport/netty4/Netty4Transport.java         | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/modules/transport-netty4/src/main/java/org/elasticsearch/transport/netty4/Netty4Transport.java b/modules/transport-netty4/src/main/java/org/elasticsearch/transport/netty4/Netty4Transport.java
index 09d843ff6be44..3cdb5a92134b7 100644
--- a/modules/transport-netty4/src/main/java/org/elasticsearch/transport/netty4/Netty4Transport.java
+++ b/modules/transport-netty4/src/main/java/org/elasticsearch/transport/netty4/Netty4Transport.java
@@ -307,15 +307,14 @@ protected Netty4TcpServerChannel bind(String name, InetSocketAddress address) {
     @SuppressForbidden(reason = "debug")
     protected void stopInternal() {
         Releasables.close(() -> {
-            Future<?> shutdownFuture = eventLoopGroup.shutdownGracefully(0, 5, TimeUnit.SECONDS);
-            shutdownFuture.awaitUninterruptibly();
-            if (shutdownFuture.isSuccess() == false) {
-                logger.warn("Error closing netty event loop group", shutdownFuture.cause());
+            if (eventLoopGroup != null) {
+                Future<?> shutdownFuture = eventLoopGroup.shutdownGracefully(0, 5, TimeUnit.SECONDS);
+                shutdownFuture.awaitUninterruptibly();
+                if (shutdownFuture.isSuccess() == false) {
+                    logger.warn("Error closing netty event loop group", shutdownFuture.cause());
+                }
             }
-
-            serverBootstraps.clear();
-            clientBootstrap = null;
-        });
+        }, serverBootstraps::clear, () -> clientBootstrap = null);
     }
 
     protected class ClientChannelInitializer extends ChannelInitializer<Channel> {