public FEELFnResult<String> invoke(@ParameterName("from") Object val) {
        if ( val == null ) {
            return FEELFnResult.ofResult( null );
        } else {
            return FEELFnResult.ofResult( TypeUtil.formatValue(val, false) );
        }
    }
@Test
    void invokeZonedDateTime() {
        final ZonedDateTime zonedDateTime = ZonedDateTime.now();
        FunctionTestUtil.assertResult(stringFunction.invoke(zonedDateTime),
                                      DateAndTimeFunction.REGION_DATETIME_FORMATTER.format(zonedDateTime));
    }