Backupmgr throws a panic after taking a backup after performing a merge of backups

1. Create a cluster with a bucket and data in it.
2. Take multiple backup of the cluster using the cbbackupmgr tool.
3. Merge all the above backups.
4. Take another backup after the merge.

We expect the backup to succeed and a message saying Backup Successfully completed must be shown to the user. But the message is not shown to the user (no message is shown) and we see panic in the backup.log file.
Attaching the backup folder with the logs.