docs: public Credential setRefreshToken(String refreshToken) {
      lock.lock();
      try {
        if (refreshToken != null) {
          Preconditions.checkArgument(jsonFactory != null && transport != null
              && clientAuthentication != null && tokenServerEncodedUrl != null,
              "Please use the Builder and call setJsonFactory, setTransport, setClientAuthentication"
              + " and setTokenServerUrl/setTokenServerEncodedUrl");
        }
        this.refreshToken = refreshToken;
      } finally {
        lock.unlock();
      }
      return this;
    }