#370: Fix the NPE by checking for null first (#371)

Add a reproducer to verify the change works and doesn't reintroduced
at a later time.

Signed-off-by: Jens Reimann <jreimann@redhat.com>

Author: ctron

org.eclipse.paho.client.mqttv3.test/src/test/java/org/eclipse/paho/client/mqttv3/test/Issue370Test.java

@@ -0,0 +1,26 @@
+/*******************************************************************************
+ * Copyright (c) 2017 Red Hat Inc.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     Red Hat Inc - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.paho.client.mqttv3.test;
+
+import org.eclipse.paho.client.mqttv3.MqttAsyncClient;
+import org.eclipse.paho.client.mqttv3.MqttException;
+import org.junit.Test;
+
+/**
+ * This is a reproducer for issue #370
+ */
+public class Issue370Test {
+    @Test
+    public void noOpenClose() throws MqttException {
+        final MqttAsyncClient client = new MqttAsyncClient("tcp://localhost", "foo-bar");
+        client.close();
+    }
+}

org.eclipse.paho.client.mqttv3/src/main/java/org/eclipse/paho/client/mqttv3/internal/ClientState.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2009, 2016 IBM Corp.
+ * Copyright (c) 2009, 2017 IBM Corp and others.
  *
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
@@ -17,6 +17,7 @@
  *    James Sutton - Ping Callback (bug 473928)
  *    Ian Craggs - fix for NPE bug 470718
  *    James Sutton - Automatic Reconnect & Offline Buffering
+ *    Jens Reimann - Fix issue #370
  */
 package org.eclipse.paho.client.mqttv3.internal;
 
@@ -1354,7 +1355,9 @@ public int getMaxInFlight(){
 	 */
 	protected void close() {
 		inUseMsgIds.clear();
-		pendingMessages.clear();
+		if (pendingMessages != null) {
+			pendingMessages.clear();
+		}
 		pendingFlows.clear();
 		outboundQoS2.clear();
 		outboundQoS1.clear();