InternalOptionalerrorEmpty property for compatibility with GraffitiObjectStreamError
The deleted object, with channels and allowed masked for the querying
actor.
A continuation may report a deletion even when the original post was not
returned by an earlier discovery, so consumers must not assume that they
previously saw this object's value.
Use this property to differentiate a tombstone from a GraffitiObjectStreamEntry.
A result from a GraffitiObjectStream that indicated an object has been deleted since the original stream was run. The original object is returned, masked to the same visibility as a discovery result.