Checkmk Werk 11780: proxmox_ve_backup_status: crash if last_backup is null

ID: 11780 Title: proxmox_ve_backup_status: crash if last_backup is null Component: Checks & agents Level: 1 Class: Bug fix Version: 2.1.0i1 In case the agent_proxmox_ve returns no backup data (last_backup is 'null' in JSON data) the parsing function would crash. This fix handles this case appropriately.