Update NettyUtils.java

Author: sigurjonviktorsson

http-clients/netty-nio-client/src/main/java/software/amazon/awssdk/http/nio/netty/internal/utils/NettyUtils.java

@@ -135,7 +135,8 @@ private static String getMessageForTooManyAcquireOperationsError() {
     public static String closedChannelMessage(Channel channel) {
         ChannelDiagnostics channelDiagnostics = channel != null && channel.attr(CHANNEL_DIAGNOSTICS) != null ?
                                                 channel.attr(CHANNEL_DIAGNOSTICS).get() : null;
-        ChannelDiagnostics parentChannelDiagnostics = channel != null && channel.parent() != null ?
+        ChannelDiagnostics parentChannelDiagnostics = channel != null && channel.parent() != null && 
+                                                      channel.parent().attr(CHANNEL_DIAGNOSTICS) != null ?
                                                       channel.parent().attr(CHANNEL_DIAGNOSTICS).get() : null;
 
         StringBuilder error = new StringBuilder();