code: function (req, res) {
      if (!req[this.paramName]) {
        return res.notFound();
      }
  
      var populations = this.filterPopulations('show');
      req[this.paramName].populate(populations, function(err, document) {
        if (err) {
          return res.handleError(err);
        }
  
        return res.ok(self.getResponseObject(document));
      })
    }
docs: Get a single document, returning the request
  property named {@link ParamController#paramName}.
  @param {IncomingMessage} req - The request message object
  @param {ServerResponse} res - The outgoing response object
  @returns {ServerResponse} A single document or NOT FOUND if no document has been found