Avoid NPE when processing response message in unit tests

The CoapAsyncRequestObserver spawns a cleaning task when an outbound
message is ready to be sent. When invoking the onResponse method in a
unit test to trigger the processing of an incoming response, a NPE is
thrown if onReadyToSend has not been invoked before.

All other methods use the private cancelCleaningTask method to stop the
cleaning task which performs a non-null check before stopping the task.
The onResponse method has been changed to also use this method in order
to prevent the NPE.

Signed-off-by: Kai Hudalla <kai.hudalla@bosch.io>

leshan-core-cf/src/main/java/org/eclipse/leshan/core/californium/CoapAsyncRequestObserver.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2016 Sierra Wireless and others.
+ * Copyright (c) 2016, 2021 Sierra Wireless and others.
  * 
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v2.0
@@ -94,7 +94,7 @@ public void onResponse(Response coapResponse) {
         LOG.debug("Received coap response: {} for {}", coapResponse, coapRequest);
         coapRequest.removeMessageObserver(this);
         if (eventRaised.compareAndSet(false, true)) {
-            cleaningTask.cancel(false);
+            cancelCleaningTask();
             try {
                 responseCallback.onResponse(coapResponse);
             } catch (RuntimeException e) {
@@ -114,8 +114,8 @@ public void onReadyToSend() {
 
     @Override
     public void onTimeout() {
-        cancelCleaningTask();
         if (eventRaised.compareAndSet(false, true)) {
+            cancelCleaningTask();
             errorCallback.onError(new TimeoutException(Type.COAP_TIMEOUT,
                     "Request %s timed out : CoAP or blockwise timeout", coapRequest.getURI()));
         } else {
@@ -126,8 +126,8 @@ public void onTimeout() {
 
     @Override
     public void onCancel() {
-        cancelCleaningTask();
         if (eventRaised.compareAndSet(false, true)) {
+            cancelCleaningTask();
             if (responseTimedOut.get()) {
                 errorCallback.onError(new TimeoutException(Type.RESPONSE_TIMEOUT,
                         "Request %s timed out : no response received", coapRequest.getURI()));
@@ -143,8 +143,8 @@ public void onCancel() {
 
     @Override
     public void onReject() {
-        cancelCleaningTask();
         if (eventRaised.compareAndSet(false, true)) {
+            cancelCleaningTask();
             errorCallback.onError(new RequestRejectedException("Request %s rejected", coapRequest.getURI()));
         } else {
             LOG.debug("OnReject callback ignored because an event was already raised for this request {}", coapRequest);
@@ -153,8 +153,8 @@ public void onReject() {
 
     @Override
     public void onSendError(Throwable error) {
-        cancelCleaningTask();
         if (eventRaised.compareAndSet(false, true)) {
+            cancelCleaningTask();
             if (error instanceof DtlsHandshakeTimeoutException) {
                 errorCallback.onError(new TimeoutException(Type.DTLS_HANDSHAKE_TIMEOUT, error,
                         "Request %s timeout : dtls handshake timeout", coapRequest.getURI()));