Bulletproof AbstractProxyServlet#destory() to make it easier to write

unit tests for custom subclasses of AbstractProxyServlet

jetty-proxy/src/main/java/org/eclipse/jetty/proxy/AbstractProxyServlet.java

@@ -145,11 +145,14 @@ public void destroy()
     {
         try
         {
-            _client.stop();
+            if (_client != null)
+                _client.stop();
         }
         catch (Exception x)
         {
-            if (_log.isDebugEnabled())
+            if (_log == null)
+                x.printStackTrace();
+            else if (_log.isDebugEnabled())
                 _log.debug("Failed to stop client", x);
         }
     }

jetty-proxy/src/test/java/org/eclipse/jetty/proxy/AbstractProxyServletTest.java

@@ -0,0 +1,39 @@
+//
+// ========================================================================
+// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+package org.eclipse.jetty.proxy;
+
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+import org.eclipse.jetty.client.api.Response.CompleteListener;
+import org.junit.jupiter.api.Test;
+
+public class AbstractProxyServletTest
+{
+
+    @Test
+    public void testNewDestroy() throws Exception
+    {
+        new AbstractProxyServlet()
+        {
+            private static final long serialVersionUID = 1L;
+
+            @Override
+            protected CompleteListener newProxyResponseListener(HttpServletRequest clientRequest, HttpServletResponse proxyResponse) 
+            {
+                return null;
+            }
+        }.destroy();
+    }
+}

jetty-proxy/src/test/java/org/eclipse/jetty/proxy/AsyncMiddleManServletTest.java

@@ -159,9 +159,18 @@ private void startClient() throws Exception
     @AfterEach
     public void dispose() throws Exception
     {
-        client.stop();
-        proxy.stop();
-        server.stop();
+        if (client != null)
+            client.stop();
+        if (proxy != null)
+            proxy.stop();
+        if (server != null)
+            server.stop();
+    }
+
+    @Test
+    public void testNewDestroy() throws Exception
+    {
+        new AsyncMiddleManServlet().destroy();
     }
 
     @Test