public List<KuduPredicate> convert(ScalarOperator operator) {
        if (operator == null) {
            return null;
        }
        return operator.accept(this, null);
    }
@Test
    public void testIsNull() {
        ScalarOperator op = new IsNullPredicateOperator(false, F0);
        List<KuduPredicate> result = CONVERTER.convert(op);
        Assert.assertEquals(result.get(0).toString(), "`f0` NONE");
    }