private fun handleOnSignInButtonPressed(ui: AnkoContext<SignInActivity>, username: String, password: String) {

if (username.isBlank() || password.isBlank()) {
    with(ui) {
      alert(title = R.string.sigIn_alert_invalid_user_title,
              message = R.string.sigIn_alert_invalid_user_message) {

        positiveButton(R.string.dialog_button_close) {}
      }.show()
    }
  } else {
    // TODO
  }