code: func (res *ResponseRecorder) WriteHeader(statusCode int) {
  	if res.statusCode == 0 { // set it only if not setted already, we don't want logs about multiple sends
  		res.statusCode = statusCode
  		res.underline.WriteHeader(statusCode)
  	}
  
  }
docs: // WriteHeader sends an HTTP response header with status code.
  // If WriteHeader is not called explicitly, the first call to Write
  // will trigger an implicit WriteHeader(http.StatusOK).
  // Thus explicit calls to WriteHeader are mainly used to
  // send error codes.