refreshToken method Null safety

void refreshToken()

Refreshes the auth token using the saved refresh token

Implementation

void refreshToken() {
  if (token == '' || refresh == '') {
    throw 'Missing auth token or refresh token, make sure you logged in through the [login] function.';
  }
  http.post(Uri.parse('https://api.mangadex.org/auth/refresh'),
      body: '"token":"$refresh"',
      headers: {
        HttpHeaders.contentTypeHeader: 'application/json',
        HttpHeaders.userAgentHeader: 'mangadex_dart_api/1.0'
      }).then((res) {
    var data = jsonDecode(res.body);
    if (res.statusCode == 200) {
      token = data['token']['session'];
      refresh = data['token']['refresh'];
    } else {
      throw 'An error has happened: ${data["errors"][0]["title"]} - ${data["errors"][0]["detail"]}';
    }
  });
}