jsonify parse -1 into undefined

[mindon]

both in main and jsr:@fresh/core@2.0.0-alpha.23

here a testing case for jsonify stringify_test.ts

Deno.test("stringify - Map with", () => {
  expect(stringify({ foo: -1 }))
    .toEqual(
      '[{"foo":1},-1]',
    );
});

while testing in parse_test.ts, it failed expecting { foo: undefined }

Deno.test("parse - -1 as undefined", () => {
  expect(parse(`[{"foo":1},-1]`)).toEqual({ foo: -1 });
});

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