DefaultPersistenceUnitManager.determineDefaultPersistenceUnitRootUrl is unable to resolve root url in native image

[christophstrobl]

Bootstrapping the DefaultPersistenceUnitManager fails in native image being unable to resolve the root url. Replacing determineDefaultPersistenceUnitRootUrl via a substitution that returns null allowed to initialize the PersistenceUnitManager.

See: pring-aot-smoke-tests#113

[jhoeller]

I guess it would also help to call setDefaultPersistenceUnitRootLocation(null) since the implementation already has that escape hatch? We should make the default implementation more defensive though, there is no need to fail hard, at least not with the ORIGINAL_DEFAULT_PERSISTENCE_UNIT_ROOT_LOCATION as input. This could be as straightforward as just logging the "Unable to resolve persistence unit root URL" message and returning null instead of throwing a PersistenceException there, potentially with an if check to only perform such a lenient return in case of defaultPersistenceUnitRootLocation == ORIGINAL_DEFAULT_PERSISTENCE_UNIT_ROOT_LOCATION.