The RHEV upgrade fails with "FATAL: Cannot execute sql command: convert_memory_snapshots_to_disks.sql"

Issue

Upgrade from RHEV 3.6 to RHV 4.x fails with following messages

psql:/usr/share/ovirt-engine/dbscripts/upgrade/04_00_0140_convert_memory_snapshots_to_disks.sql:97: ERROR:  null value in column "size" violates not-null constraint
DETAIL:  Failing row contains (325fa017-2771-4516-a01d-806edf781cd6, 2018-10-05 17:33:30.65685+01, null, 00000000-0000-0000-0000-000000000000, null, 1, null, null, 0, 5, 0d53d2c3-491f-4646-9c0d-a592aeae5ff5, 2018-10-05 17:33:30.65685+01, null, f, null).
FATAL: Cannot execute sql command: --file=/usr/share/ovirt-engine/dbscripts/upgrade/04_00_0140_convert_memory_snapshots_to_disks.sql

2018-10-05 17:33:30,681+0100 ERROR otopi.plugins.ovirt_engine_setup.ovirt_engine.db.schema schema._misc:338 schema.sh: FATAL: Cannot execute sql command: --file=/usr/share/ovirt-engine/dbscripts/upgrade/04_00_0140_convert_memory_snapshots_to_disks.sql
2018-10-05 17:33:30,682+0100 DEBUG otopi.context context._executeMethod:143 method exception
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/otopi/context.py", line 133, in _executeMethod
    method['method']()
  File "/usr/share/ovirt-engine/setup/bin/../plugins/ovirt-engine-setup/ovirt-engine/db/schema.py", line 340, in _misc
    raise RuntimeError(_('Engine schema refresh failed'))
RuntimeError: Engine schema refresh failed