protected void enableCheckButtonIfReady() {
        binding.check.setEnabled(StringUtils.isNotEmpty(binding.username.getText()) &&
                StringUtils.isNotEmpty(binding.password.getText()));
    }
Enable or disable the start button depending on login/password field.
If both fields are not empty, button is enabled.
main/src/main/java/cgeo/geocaching/settings/AbstractCredentialsAuthorizationActivity.java