public static Expression sanitize(Expression expr) {
    return ExpressionVisitors.visit(expr, new ExpressionSanitizer());
  }
@Test
  public void testUnchangedUnaryPredicates() {
    for (Expression unary :
        Lists.newArrayList(
            Expressions.isNull("test"),
            Expressions.notNull("test"),
            Expressions.isNaN("test"),
            Expressions.notNaN("test"))) {
      assertEquals(unary, ExpressionUtil.sanitize(unary));
      assertEquals(unary, ExpressionUtil.sanitize(FLOAT_TEST, unary, true));
    }
  }