code: public WriteResult<T, K> save(T object, WriteConcern concern) throws MongoException {
          DBObject dbObject = convertToDbObject(object);
          return new WriteResult<T, K>(this, dbCollection.save(dbObject, concern), dbObject);
      }
docs: Saves an object to this collection (does insert or update based on the object _id).
  
  @param object  the <code>DBObject</code> to save
  @param concern the write concern
  @return The result
  @throws MongoException If an error occurred