Provisional API: This interface is part of an interim API that is still
under development and expected to change significantly before reaching
stability.
Provisional API: This interface is part of an interim API that is still
under development and expected to change significantly before reaching
stability.
Return whether the underlying resource exists for the MappingFilePersistenceUnitDefaults object
If there is a node in the orm.xml file for persistence-unit-default, this returns true, otherwise false.