EntryEvent TKey, TValue  OldValue Property Pivotal GemFire .NET Client Documentation
Returns 'null' if there was no value in the cache. If the prior state of the entry was invalid, or non-existent/destroyed, then the old value will be 'null'.

Namespace: GemStone.GemFire.Cache.Generic
Assembly: GemStone.GemFire.Cache (in GemStone.GemFire.Cache.dll) Version: 8.1.0.0
Syntax

public TValue OldValue { get; }
See Also