Creating snapshots during installation a second time shows errors

[Mark-H]

Iterating over Resources and storing snapshots..
Error creating snapshot for Resource 2
Error creating snapshot for Resource 3
Error creating snapshot for Resource 5
Error creating snapshot for Resource 6
Error creating snapshot for Resource 7

Seems to be due to DelteManager::createDelta retrieving the previous delta, not finding any changes, and returning null in line 157.