code: def fetch
          response = client.fetch_object(parse_class, id)
          return nil if response.error?
          response.result
        end
docs: This method is a general implementation that gets overriden by Parse::Object subclass.
   Given the class name and the id, we will go to Parse and fetch the actual record, returning the
   JSON object.
   @return [Parse::Object] the fetched Parse::Object, nil otherwise.