Fix NPE in metrics collector if channel is null

Fixes #944

(cherry picked from commit 20e641e)

Author: acogoluegnes

Diff for: src/main/java/com/rabbitmq/client/impl/AMQConnection.java

@@ -1,4 +1,4 @@
-// Copyright (c) 2007-2020 VMware, Inc. or its affiliates.  All rights reserved.
+// Copyright (c) 2007-2023 VMware, Inc. or its affiliates.  All rights reserved.
 //
 // This software, the RabbitMQ Java client library, is triple-licensed under the
 // Mozilla Public License 2.0 ("MPL"), the GNU General Public License version 2
@@ -605,7 +605,9 @@ public Channel createChannel(int channelNumber) throws IOException {
         ChannelManager cm = _channelManager;
         if (cm == null) return null;
         Channel channel = cm.createChannel(this, channelNumber);
-        metricsCollector.newChannel(channel);
+        if (channel != null) {
+            metricsCollector.newChannel(channel);
+        }
         return channel;
     }
 
@@ -616,7 +618,9 @@ public Channel createChannel() throws IOException {
         ChannelManager cm = _channelManager;
         if (cm == null) return null;
         Channel channel = cm.createChannel(this);
-        metricsCollector.newChannel(channel);
+        if (channel != null) {
+            metricsCollector.newChannel(channel);
+        }
         return channel;
     }
 

Diff for: src/main/java/com/rabbitmq/client/impl/AbstractMetricsCollector.java

@@ -72,12 +72,14 @@ public void closeConnection(Connection connection) {
 
     @Override
     public void newChannel(final Channel channel) {
-        try {
-            incrementChannelCount(channel);
-            channel.addShutdownListener(cause -> closeChannel(channel));
-            connectionState(channel.getConnection()).channelState.put(channel.getChannelNumber(), new ChannelState(channel));
-        } catch(Exception e) {
-            LOGGER.info("Error while computing metrics in newChannel: " + e.getMessage());
+        if (channel != null) {
+            try {
+                incrementChannelCount(channel);
+                channel.addShutdownListener(cause -> closeChannel(channel));
+                connectionState(channel.getConnection()).channelState.put(channel.getChannelNumber(), new ChannelState(channel));
+            } catch(Exception e) {
+                LOGGER.info("Error while computing metrics in newChannel: " + e.getMessage());
+            }
         }
     }