java MongoDB RenameCollection

private DBCollection renameCollection(String oldCollection, String newCollection) {
if (!mongoTemplate.collectionExists(oldCollection))
return null;
if (mongoTemplate.collectionExists(newCollection))
mongoTemplate.dropCollection(newCollection);
DB db = mongoTemplate.getDb();
DBCollection dbCollection = db.getCollection(oldCollection);
return dbCollection.rename(newCollection, true);
}