CLOUDSTACK-8525: NPE while updating the state of the volume after deletion

The volume is already deleted (may be by the cleanup thread) and hence
the NPE. Added a not null check for the volumevo and returning false
from the state transition

This closes #321

engine/storage/volume/src/org/apache/cloudstack/storage/volume/VolumeObject.java

@@ -178,8 +178,10 @@ public class VolumeObject implements VolumeInfo {
         boolean result = false;
         try {
             volumeVO = volumeDao.findById(volumeVO.getId());
-            result = _volStateMachine.transitTo(volumeVO, event, null, volumeDao);
-            volumeVO = volumeDao.findById(volumeVO.getId());
+            if(volumeVO != null) {
+                result = _volStateMachine.transitTo(volumeVO, event, null, volumeDao);
+                volumeVO = volumeDao.findById(volumeVO.getId());
+            }
         } catch (NoTransitionException e) {
             String errorMessage = "Failed to transit volume: " + getVolumeId() + ", due to: " + e.toString();
             s_logger.debug(errorMessage);

engine/storage/volume/test/org/apache/cloudstack/storage/volume/VolumeObjectTest.java

@@ -0,0 +1,77 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.cloudstack.storage.volume;
+
+import org.apache.cloudstack.engine.subsystem.api.storage.DataStore;
+import org.apache.cloudstack.storage.datastore.ObjectInDataStoreManager;
+import org.apache.cloudstack.storage.datastore.db.VolumeDataStoreDao;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.Mockito;
+import org.mockito.runners.MockitoJUnitRunner;
+
+import com.cloud.storage.Storage;
+import com.cloud.storage.Volume;
+import com.cloud.storage.VolumeVO;
+import com.cloud.storage.dao.DiskOfferingDao;
+import com.cloud.storage.dao.VolumeDao;
+import com.cloud.vm.dao.VMInstanceDao;
+
+@RunWith(MockitoJUnitRunner.class)
+public class VolumeObjectTest {
+
+    @Mock
+    VolumeDao volumeDao;
+
+    @Mock
+    VolumeDataStoreDao volumeStoreDao;
+
+    @Mock
+    ObjectInDataStoreManager objectInStoreMgr;
+
+    @Mock
+    VMInstanceDao vmInstanceDao;
+
+    @Mock
+    DiskOfferingDao diskOfferingDao;
+
+    @InjectMocks
+    VolumeObject volumeObject;
+
+    @Before
+    public void setUp() throws Exception {
+        volumeObject.configure(Mockito.mock(DataStore.class), new VolumeVO("name", 1l, 1l, 1l, 1l, 1l, "folder", "path", Storage.ProvisioningType.THIN, 1l, Volume.Type.DATADISK));
+    }
+
+    /**
+     * Tests the following scenario:
+     * If the volume gets deleted by another thread (cleanup) and the cleanup is attempted again, the volume isnt found in DB and hence NPE occurs
+     * during transition
+     */
+    @Test
+    public void testStateTransit() {
+        boolean result = volumeObject.stateTransit(Volume.Event.OperationFailed);
+        Assert.assertFalse("since the volume doesnt exist in the db, the operation should fail but, should not throw any exception", result);
+    }
+}