public static Expression generateFilterExpression(SearchArgument sarg) {
    return translate(sarg.getExpression(), sarg.getLeaves());
  }
@Test
  public void testIsNullOperand() {
    SearchArgument.Builder builder = SearchArgumentFactory.newBuilder();
    SearchArgument arg = builder.startAnd().isNull("salary", PredicateLeaf.Type.LONG).end().build();

    UnboundPredicate expected = Expressions.isNull("salary");
    UnboundPredicate actual =
        (UnboundPredicate) HiveIcebergFilterFactory.generateFilterExpression(arg);

    assertThat(expected.op()).isEqualTo(actual.op());
    assertThat(expected.ref().name()).isEqualTo(actual.ref().name());
  }