* @return an OptionalThing containing the Config if the field exists and has a non-blank value,
     *         otherwise an empty OptionalThing
     */
    public OptionalThing<Config> getConfig(final String fieldName) {
        final String value = params.get(fieldName);
        if (StringUtil.isNotBlank(value)) {
            return OptionalThing.of(new Config(value));
        }

        assertTrue(fieldConfigs.getConfig("test").isEmpty());
    }

    @Test
    public void test_values() {
        final Map<String, String> params = Maps.of("foo", "bar");
        FieldConfigs fieldConfigs = new FieldConfigs(params);
        assertTrue(fieldConfigs.getConfig("test").isEmpty());
        assertFalse(fieldConfigs.getConfig("foo").isEmpty());