Shell: add missing null check. Fixes #1711.
Merge pull request #1708 from tinwelint/2.0-cement-master

Uses a snapshot of the reference to Master instead of a proxy
Merge pull request #1712 from jotomo/1711

Shell: add missing null check. Fixes #1711.
Fixes #1697

Fixes #1697 which is an issue where replacing a property on an entity
using batch inserter where the property would be bigger than the one it
overwrote so that it would need to go into a new property record. There
would be a NullPointerException due to removing that property block from
the property record two times.