Null

Filter::field('age', [FilterType::NULL]);
Filter::field('weight', [FilterType::NULL]);

$filters = [
    [
        'type'   => '$null',
        'target' => 'age',
        'value'  => true,
    ],
    [
        'type'   => '$null',
        'target' => 'weight',
        'value'  => false,
    ],
];

$sql = Person::filter($filters)->toRawSql();

select *
  from "people"
 where "people"."age" is null
   and "people"."weight" is not null