Function filter

tests/qs/stringify.test.ts:1933–1935

(_prefix, value)

  test('strictNullHandling works with custom filter', function () {
    // @ts-expect-error
    var filter = function (_prefix, value) {
      return value;
    };

    var options = { strictNullHandling: true, filter: filter };
    // st.equal(stringify({ key: null }, options), 'key');