server: fix null pointer on powerflex attach volume edge case (#7498)

This PR fixes a null pointer edge case where a PowerFlex volume is attached to a VM.

In this edge case, a VM has been created, started, stopped, and then reimaged. VM has a last host ID but the newly attached volume does not yet have a storage pool assigned, it will be assigned on the VM start. However, we assume that if the VM's host is not null, we need to try to revoke access to the volume for the host. Since there is no storage pool yet for the volume, we hit a null pointer when checking to see if the volume's pool is PowerFlex.

This was affecting all storage types, I could reproduce it with local storage, since the null pointer is at the check for pool's type.

Co-authored-by: Marcus Sorensen <mls@apple.com>

Author: Marcus Sorensen

server/src/main/java/com/cloud/storage/VolumeApiServiceImpl.java

@@ -4260,7 +4260,7 @@ private VolumeVO sendAttachVolumeCommand(UserVmVO vm, VolumeVO volumeToAttach, L
                         _volsDao.update(volumeToAttach.getId(), volumeToAttach);
                     }
 
-                    if (host != null && volumeToAttachStoragePool.getPoolType() == Storage.StoragePoolType.PowerFlex) {
+                    if (host != null && volumeToAttachStoragePool != null && volumeToAttachStoragePool.getPoolType() == Storage.StoragePoolType.PowerFlex) {
                         // Unmap the volume on PowerFlex/ScaleIO pool for stopped VM
                         volService.revokeAccess(volFactory.getVolume(volumeToAttach.getId()), host, dataStore);
                     }