code: function(instance) {
      var result = this._related(instance);
      if (result === undefined) {
        throw new Error(util.format('The relation "%s" has not yet been ' +
          'loaded.', this._name));
      }
      return result;
    }
docs: The item property for this relation.
  
  This property allows access to the cached object that has been fetched
  for a specific model in a given relation. Before the cache has been
  filled, accessing this property will throw an exception.
  
  It is accessible on an individual model via `<singular>` and via
  `get<Singular>`. For instance, an article that belongs to an author would
  cause this method to get triggered via `article.author` or
  `article.getAuthor`.
  
  The naming conventions are set forth in {@link BelongsTo#overrides}.
  
  @method
  @protected
  @param {Model} instance The model instance on which to operate.
  @see {@link BaseRelation#methods}