code: public function get($key)
      {
          if (!$this->repository->containsKey($key))
              throw new ReferenceDoesNotExistException();
          return $this->repository->get($key);
      }
docs: Retrieves a reference identified by key
  
  @param $key
  @return mixed
  @throws ReferenceDoesNotExistException if no reference exists identified by specified key