The Database property returns the database object which contains the MTPIProperty.
The object placeholder is an object expression that evaluates to a MTPIProperty object.
Since an MTPIProperty is only contained in an MTPIProperties collection that is part of a PIAnnotation, it has no database, so this property will always return an error and the returned Database will be NULL.
MTPIProperties & MTPIProperty are free-threaded versions of PIProperties and PIProperty respectively. They emulate the non-free threaded versions.