code: func sendError(rw http.ResponseWriter, code int, err error) {
  	resp := errorResponse{Error: errorEntity{Code: code}}
  	if err != nil {
  		resp.Error.Message = err.Error()
  	}
  	sendResponse(rw, code, resp)
  }
docs: // sendError builds an errorResponse entity from the given arguments, serializing
  // the object into the provided http.ResponseWriter