@Override
public synchronized void loadOntologies(OntologyProvider<?> loader) {
if (loader == null) throw new IllegalArgumentException("A null loader is not allowed.");
for (RegistryItem item : getChildren()) {
if (item instanceof RegistryOntology) {
RegistryOntology o = (RegistryOntology) item;
IRI id = o.getIRI();
try {
// No preferred key, we don't have a prefix here.
String key = loader.loadInStore(id, null, null, false);
if (key == null || key.isEmpty()) log.error(
"Empty storage key. Ontology {} was apparently not stored.", id);