[PMT-2963] plesk-migrator fails with "Cause: 'NoneType' object is not iterable"

Environment:
1. Both src & target were running at the time Plesk 12.5.30 Update #39 with Plesk Migrator 1.12.3
2. OS:
- src: CentOS release 5.11 (Final) 64bit as Virtuozzo container
- target: CentOS Linux release 7.2.1511 (Core) as Xen domU

While testing a full Plesk->Plesk server migration from cli I'm getting this "critical" error:
[2016-07-08 08:32:53][INFO] ******************** Summary ********************
[2016-07-08 08:32:53][INFO] Operation finished successfully for 6 out of 6...

[PMT-2963] plesk-migrator fails with "Cause: 'NoneType' object is not iterable"