protected static RDFNode getUnique(Resource root, Property property) {
List<RDFNode> nodes = root.listProperties(property).mapWith(getObject).toList();
if (nodes.size() == 0) return null;
if (nodes.size() == 1) return nodes.get(0);
throw new NotUniqueException(root, property);
}
protected static Statement getUniqueStatement(Resource root, Property property) {
List<Statement> statements = root.listProperties(property).toList();
if (statements.size() == 0) return null;
if (statements.size() == 1) return statements.get(0);
throw new NotUniqueException(root, property);
}