Created attachment 1728640 [details]
logs

Description of problem:
Multiple NullPointerExceptions [1] are seen on the engine log when removing the VM which was previously fully backed up, and its backup checkpoints were removed.
As we are not sure what are the consequences of those exceptions, a customer might get a feeling that some disastrous event had just took place.

Version-Release number of selected component (if applicable):
rhv-release-4.4.3-13-001.noarch
libvirt-6.6.0-6.module
vdsm-4.40.35.1-1.el8ev.x86_64


How reproducible:
100%

Steps to Reproduce:
0. Enable incrementalbackup feature on the engine:
engine-config -s "IsIncrementalBackupSupported=true" --cver 4.5 && systemctl restart ovirt-engine
1. Create a VM from template and start it
2. Make a full backup of its disks + Check that a checkpoint is created
3. Run SDK example script for removing the root checkpoint (make sure first to create a config file required for the script in /root/.config/ovirt.conf:
$ Python3 remove_checkpoint.py <VM uuid> -c engine
4. Remove the VM

Actual results:
VM removed, but many NullPointerExceptions are seen in the engine log

Expected results:
No NullPointerExceptions should appear

Additional info:
Attaching log of engine.log vdsm.log libvirt.log in debug level.
Note that in those logs, the backup and checkpoints removal was done twice. But in order to reproduce it, once is enough.

[1]:
2020-11-12 09:08:28,030+02 INFO  [org.ovirt.engine.core.bll.tasks.AsyncTaskManager] (default task-32) [vms_delete_8e8db172-5248-4aab
] Adding task '87a6d0d8-6c49-4937-9faf-d71259820f72' (Parent Command 'RemoveVm', Parameters Type 'org.ovirt.engine.core.common.async
tasks.AsyncTaskParameters'), polling hasn't started yet..
2020-11-12 09:08:28,043+02 ERROR [org.ovirt.engine.core.bll.CommandsFactory] (EE-ManagedScheduledExecutorService-engineScheduledThreadPool-Thread-89) [84900f53-bff9-4d50-94c6-95fc17a1def3] An exception has occurred while trying to create a command object for command 'DeleteVmCheckpoint' with parameters 'VmCheckpointParameters:{commandId='1065e5ee-2b42-4cc0-ade2-4c8c9b693959', user='admin', commandType='Unknown', vmId='399891fe-e891-4791-a822-5eb1a2e22c3b'}': WELD-000049: Unable to invoke protected final void org.ovirt.engine.core.bll.CommandBase.postConstruct() on org.ovirt.engine.core.bll.DeleteVmCheckpointCommand@1264be5d
2020-11-12 09:08:28,043+02 ERROR [org.ovirt.engine.core.bll.CommandsFactory] (EE-ManagedScheduledExecutorService-engineScheduledThreadPool-Thread-89) [84900f53-bff9-4d50-94c6-95fc17a1def3] Exception: java.lang.NullPointerException
        at deployment.engine.ear.bll.jar//org.ovirt.engine.core.bll.DeleteVmCheckpointCommand.init(DeleteVmCheckpointCommand.java:74)
        at deployment.engine.ear.bll.jar//org.ovirt.engine.core.bll.CommandBase.postConstruct(CommandBase.java:218)
        at jdk.internal.reflect.GeneratedMethodAccessor147.invoke(Unknown Source)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        at org.jboss.weld.core.4.Final-redhat-00001//org.jboss.weld.injection.producer.DefaultLifecycleCallbackInvoker.invokeMethods(DefaultLifecycleCallbackInvoker.java:83)
        at org.jboss.weld.core.4.Final-redhat-00001//org.jboss.weld.injection.producer.DefaultLifecycleCallbackInvoker.postConstruct(DefaultLifecycleCallbackInvoker.java:66)
        at org.jboss.weld.core.4.Final-redhat-00001//org.jboss.weld.injection.producer.BasicInjectionTarget.postConstruct(BasicInjectionTarget.java:122)
        at deployment.engine.ear//org.ovirt.engine.core.di.Injector.injectMembers(Injector.java:41)
        at deployment.engine.ear.bll.jar//org.ovirt.engine.core.bll.CommandsFactory.createCommand(CommandsFactory.java:104)
        at deployment.engine.ear.bll.jar//org.ovirt.engine.core.bll.tasks.CommandsRepository.retrieveCommand(CommandsRepository.java:167)
        at deployment.engine.ear.bll.jar//org.ovirt.engine.core.bll.tasks.CommandsRepository.retrieveCommand(CommandsRepository.java:154)
        at deployment.engine.ear.bll.jar//org.ovirt.engine.core.bll.tasks.CommandCoordinatorImpl.retrieveCommand(CommandCoordinatorImpl.java:127)
        at deployment.engine.ear.bll.jar//org.ovirt.engine.core.bll.tasks.CommandCoordinatorUtil.retrieveCommand(CommandCoordinatorUtil.java:309)
        at deployment.engine.ear.bll.jar//org.ovirt.engine.core.bll.ChildCommandsCallbackBase.getCommand(ChildCommandsCallbackBase.java:189)
        at deployment.engine.ear.bll.jar//org.ovirt.engine.core.bll.ChildCommandsCallbackBase.onSucceeded(ChildCommandsCallbackBase