diff --git a/Test/EmptyResp.dart b/Test/EmptyResp.dart
index b35f5ff..46c038a 100644
--- a/Test/EmptyResp.dart
+++ b/Test/EmptyResp.dart
@@ -1,15 +1,16 @@
 import 'dart:convert' show json;
 
 class EmptyResp {
-  Qwe qwe;
+  Qwe? qwe;
 
   EmptyResp.fromParams({this.qwe});
 
-  factory EmptyResp(jsonStr) => jsonStr == null
-      ? null
-      : jsonStr is String
-          ? EmptyResp.fromJson(json.decode(jsonStr))
-          : EmptyResp.fromJson(jsonStr);
+  factory EmptyResp(Object jsonStr) => jsonStr is String
+      ? EmptyResp.fromJson(json.decode(jsonStr))
+      : EmptyResp.fromJson(jsonStr);
+
+  static EmptyResp? parse(jsonStr) =>
+      ['null', '', null].contains(jsonStr) ? null : EmptyResp(jsonStr);
 
   EmptyResp.fromJson(jsonRes) {
     qwe = jsonRes['qwe'] == null ? null : Qwe.fromJson(jsonRes['qwe']);
@@ -19,12 +20,14 @@ class EmptyResp {
   String toString() {
     return '{"qwe": $qwe}';
   }
+
+  String toJSON() => this.toString();
 }
 
 class Qwe {
-  List<dynamic> asd;
-  List<Object> qaz;
-  List<dynamic> zxc;
+  List<dynamic?>? asd;
+  List<Object?>? qaz;
+  List<dynamic?>? zxc;
 
   Qwe.fromParams({this.asd, this.qaz, this.zxc});
 
@@ -32,19 +35,19 @@ class Qwe {
     asd = jsonRes['asd'] == null ? null : [];
 
     for (var asdItem in asd == null ? [] : jsonRes['asd']) {
-      asd.add(asdItem);
+      asd!.add(asdItem);
     }
 
     qaz = jsonRes['qaz'] == null ? null : [];
 
     for (var qazItem in qaz == null ? [] : jsonRes['qaz']) {
-      qaz.add(qazItem);
+      qaz!.add(qazItem);
     }
 
     zxc = jsonRes['zxc'] == null ? null : [];
 
     for (var zxcItem in zxc == null ? [] : jsonRes['zxc']) {
-      zxc.add(zxcItem);
+      zxc!.add(zxcItem);
     }
   }
 
@@ -52,4 +55,6 @@ class Qwe {
   String toString() {
     return '{"asd": $asd, "qaz": $qaz, "zxc": $zxc}';
   }
+
+  String toJSON() => this.toString();
 }
diff --git a/Test/IgnoreMapResp.dart b/Test/IgnoreMapResp.dart
index 34f1c46..b2c8975 100644
--- a/Test/IgnoreMapResp.dart
+++ b/Test/IgnoreMapResp.dart
@@ -1,15 +1,16 @@
 import 'dart:convert' show json;
 
 class IgnoreMapResp {
-  Data data;
+  Data? data;
 
   IgnoreMapResp.fromParams({this.data});
 
-  factory IgnoreMapResp(jsonStr) => jsonStr == null
-      ? null
-      : jsonStr is String
-          ? IgnoreMapResp.fromJson(json.decode(jsonStr))
-          : IgnoreMapResp.fromJson(jsonStr);
+  factory IgnoreMapResp(Object jsonStr) => jsonStr is String
+      ? IgnoreMapResp.fromJson(json.decode(jsonStr))
+      : IgnoreMapResp.fromJson(jsonStr);
+
+  static IgnoreMapResp? parse(jsonStr) =>
+      ['null', '', null].contains(jsonStr) ? null : IgnoreMapResp(jsonStr);
 
   IgnoreMapResp.fromJson(jsonRes) {
     data = jsonRes['data'] == null ? null : Data.fromJson(jsonRes['data']);
@@ -19,16 +20,18 @@ class IgnoreMapResp {
   String toString() {
     return '{"data": $data}';
   }
+
+  String toJSON() => this.toString();
 }
 
 class Data {
-  int wc;
-  String author;
-  String content;
-  String digest;
-  String title;
-  Map<String, dynamic> date;
-  Extra extra;
+  int? wc;
+  String? author;
+  String? content;
+  String? digest;
+  String? title;
+  Map<String, dynamic>? date;
+  Extra? extra;
 
   Data.fromParams(
       {this.wc,
@@ -53,12 +56,14 @@ class Data {
   String toString() {
     return '{"wc": $wc, "author": ${author != null ? '${json.encode(author)}' : 'null'}, "content": ${content != null ? '${json.encode(content)}' : 'null'}, "digest": ${digest != null ? '${json.encode(digest)}' : 'null'}, "title": ${title != null ? '${json.encode(title)}' : 'null'}, "date": ${date != null ? '${json.encode(date)}' : 'null'}, "extra": $extra}';
   }
+
+  String toJSON() => this.toString();
 }
 
 class Extra {
-  int a;
-  int b;
-  int c;
+  int? a;
+  int? b;
+  int? c;
 
   Extra.fromParams({this.a, this.b, this.c});
 
@@ -72,4 +77,6 @@ class Extra {
   String toString() {
     return '{"a": $a, "b": $b, "c": $c}';
   }
+
+  String toJSON() => this.toString();
 }
diff --git a/Test/ListTopResp.dart b/Test/ListTopResp.dart
index 3c65f94..f35ca02 100644
--- a/Test/ListTopResp.dart
+++ b/Test/ListTopResp.dart
@@ -1,21 +1,22 @@
 import 'dart:convert' show json;
 
 class ListTopResp {
-  List<Resp> list;
+  List<Resp?>? list;
 
   ListTopResp.fromParams({this.list});
 
-  factory ListTopResp(jsonStr) => jsonStr == null
-      ? null
-      : jsonStr is String
-          ? ListTopResp.fromJson(json.decode(jsonStr))
-          : ListTopResp.fromJson(jsonStr);
+  factory ListTopResp(Object jsonStr) => jsonStr is String
+      ? ListTopResp.fromJson(json.decode(jsonStr))
+      : ListTopResp.fromJson(jsonStr);
+
+  static ListTopResp? parse(jsonStr) =>
+      ['null', '', null].contains(jsonStr) ? null : ListTopResp(jsonStr);
 
   ListTopResp.fromJson(jsonRes) {
     list = jsonRes == null ? null : [];
 
     for (var listItem in list == null ? [] : jsonRes) {
-      list.add(listItem == null ? null : Resp.fromJson(listItem));
+      list!.add(listItem == null ? null : Resp.fromJson(listItem));
     }
   }
 
@@ -23,11 +24,13 @@ class ListTopResp {
   String toString() {
     return '{"json_list": $list}';
   }
+
+  String toJSON() => this.toString();
 }
 
 class Resp {
-  String a;
-  String b;
+  String? a;
+  String? b;
 
   Resp.fromParams({this.a, this.b});
 
@@ -40,4 +43,6 @@ class Resp {
   String toString() {
     return '{"a": ${a != null ? '${json.encode(a)}' : 'null'}, "b": ${b != null ? '${json.encode(b)}' : 'null'}}';
   }
+
+  String toJSON() => this.toString();
 }
diff --git a/Test/ListWithStringResp.dart b/Test/ListWithStringResp.dart
index e5e5b44..94f08bf 100644
--- a/Test/ListWithStringResp.dart
+++ b/Test/ListWithStringResp.dart
@@ -1,39 +1,40 @@
 import 'dart:convert' show json;
 
 class ListWithStringResp {
-  List<String> asd;
-  List<List<String>> qaz;
-  List<Qwe> zxc;
+  List<String?>? asd;
+  List<List<String?>?>? qaz;
+  List<Qwe?>? zxc;
 
   ListWithStringResp.fromParams({this.asd, this.qaz, this.zxc});
 
-  factory ListWithStringResp(jsonStr) => jsonStr == null
-      ? null
-      : jsonStr is String
-          ? ListWithStringResp.fromJson(json.decode(jsonStr))
-          : ListWithStringResp.fromJson(jsonStr);
+  factory ListWithStringResp(Object jsonStr) => jsonStr is String
+      ? ListWithStringResp.fromJson(json.decode(jsonStr))
+      : ListWithStringResp.fromJson(jsonStr);
+
+  static ListWithStringResp? parse(jsonStr) =>
+      ['null', '', null].contains(jsonStr) ? null : ListWithStringResp(jsonStr);
 
   ListWithStringResp.fromJson(jsonRes) {
     asd = jsonRes['asd'] == null ? null : [];
 
     for (var asdItem in asd == null ? [] : jsonRes['asd']) {
-      asd.add(asdItem);
+      asd!.add(asdItem);
     }
 
     qaz = jsonRes['qaz'] == null ? null : [];
 
     for (var qazItem in qaz == null ? [] : jsonRes['qaz']) {
-      List<String> qazChild = qazItem == null ? null : [];
+      List<String?>? qazChild = qazItem == null ? null : [];
       for (var qazItemItem in qazChild == null ? [] : qazItem) {
-        qazChild.add(qazItemItem);
+        qazChild!.add(qazItemItem);
       }
-      qaz.add(qazChild);
+      qaz!.add(qazChild);
     }
 
     zxc = jsonRes['zxc'] == null ? null : [];
 
     for (var zxcItem in zxc == null ? [] : jsonRes['zxc']) {
-      zxc.add(zxcItem == null ? null : Qwe.fromJson(zxcItem));
+      zxc!.add(zxcItem == null ? null : Qwe.fromJson(zxcItem));
     }
   }
 
@@ -41,10 +42,12 @@ class ListWithStringResp {
   String toString() {
     return '{"asd": ${asd != null ? '${json.encode(asd)}' : 'null'}, "qaz": ${qaz != null ? '${json.encode(qaz)}' : 'null'}, "zxc": $zxc}';
   }
+
+  String toJSON() => this.toString();
 }
 
 class Qwe {
-  String qwe;
+  String? qwe;
 
   Qwe.fromParams({this.qwe});
 
@@ -56,4 +59,6 @@ class Qwe {
   String toString() {
     return '{"qwe": ${qwe != null ? '${json.encode(qwe)}' : 'null'}}';
   }
+
+  String toJSON() => this.toString();
 }
diff --git a/Test/ListsResp.dart b/Test/ListsResp.dart
index ebcbe38..2f33a6f 100644
--- a/Test/ListsResp.dart
+++ b/Test/ListsResp.dart
@@ -1,52 +1,53 @@
 import 'dart:convert' show json;
 
 class ListsResp {
-  List<List<List<int>>> asd;
-  List<int> qaz;
-  List<List<List<Zxc>>> qwe;
+  List<List<List<int?>?>?>? asd;
+  List<int?>? qaz;
+  List<List<List<Zxc?>?>?>? qwe;
 
   ListsResp.fromParams({this.asd, this.qaz, this.qwe});
 
-  factory ListsResp(jsonStr) => jsonStr == null
-      ? null
-      : jsonStr is String
-          ? ListsResp.fromJson(json.decode(jsonStr))
-          : ListsResp.fromJson(jsonStr);
+  factory ListsResp(Object jsonStr) => jsonStr is String
+      ? ListsResp.fromJson(json.decode(jsonStr))
+      : ListsResp.fromJson(jsonStr);
+
+  static ListsResp? parse(jsonStr) =>
+      ['null', '', null].contains(jsonStr) ? null : ListsResp(jsonStr);
 
   ListsResp.fromJson(jsonRes) {
     asd = jsonRes['asd'] == null ? null : [];
 
     for (var asdItem in asd == null ? [] : jsonRes['asd']) {
-      List<List<int>> asdChild = asdItem == null ? null : [];
+      List<List<int?>?>? asdChild = asdItem == null ? null : [];
       for (var asdItemItem in asdChild == null ? [] : asdItem) {
-        List<int> asdChildChild = asdItemItem == null ? null : [];
+        List<int?>? asdChildChild = asdItemItem == null ? null : [];
         for (var asdItemItemItem in asdChildChild == null ? [] : asdItemItem) {
-          asdChildChild.add(asdItemItemItem);
+          asdChildChild!.add(asdItemItemItem);
         }
-        asdChild.add(asdChildChild);
+        asdChild!.add(asdChildChild);
       }
-      asd.add(asdChild);
+      asd!.add(asdChild);
     }
 
     qaz = jsonRes['qaz'] == null ? null : [];
 
     for (var qazItem in qaz == null ? [] : jsonRes['qaz']) {
-      qaz.add(qazItem);
+      qaz!.add(qazItem);
     }
 
     qwe = jsonRes['qwe'] == null ? null : [];
 
     for (var qweItem in qwe == null ? [] : jsonRes['qwe']) {
-      List<List<Zxc>> qweChild = qweItem == null ? null : [];
+      List<List<Zxc?>?>? qweChild = qweItem == null ? null : [];
       for (var qweItemItem in qweChild == null ? [] : qweItem) {
-        List<Zxc> qweChildChild = qweItemItem == null ? null : [];
+        List<Zxc?>? qweChildChild = qweItemItem == null ? null : [];
         for (var qweItemItemItem in qweChildChild == null ? [] : qweItemItem) {
-          qweChildChild.add(
+          qweChildChild!.add(
               qweItemItemItem == null ? null : Zxc.fromJson(qweItemItemItem));
         }
-        qweChild.add(qweChildChild);
+        qweChild!.add(qweChildChild);
       }
-      qwe.add(qweChild);
+      qwe!.add(qweChild);
     }
   }
 
@@ -54,10 +55,12 @@ class ListsResp {
   String toString() {
     return '{"asd": $asd, "qaz": $qaz, "qwe": $qwe}';
   }
+
+  String toJSON() => this.toString();
 }
 
 class Zxc {
-  int zxc;
+  int? zxc;
 
   Zxc.fromParams({this.zxc});
 
@@ -69,4 +72,6 @@ class Zxc {
   String toString() {
     return '{"zxc": $zxc}';
   }
+
+  String toJSON() => this.toString();
 }
diff --git a/Test/RegionResp.dart b/Test/RegionResp.dart
index a91b89d..278ce27 100644
--- a/Test/RegionResp.dart
+++ b/Test/RegionResp.dart
@@ -1,18 +1,19 @@
 import 'dart:convert' show json;
 
 class RegionResp {
-  int code;
-  int ttl;
-  String message;
-  Data data;
+  int? code;
+  int? ttl;
+  String? message;
+  Data? data;
 
   RegionResp.fromParams({this.code, this.ttl, this.message, this.data});
 
-  factory RegionResp(jsonStr) => jsonStr == null
-      ? null
-      : jsonStr is String
-          ? RegionResp.fromJson(json.decode(jsonStr))
-          : RegionResp.fromJson(jsonStr);
+  factory RegionResp(Object jsonStr) => jsonStr is String
+      ? RegionResp.fromJson(json.decode(jsonStr))
+      : RegionResp.fromJson(jsonStr);
+
+  static RegionResp? parse(jsonStr) =>
+      ['null', '', null].contains(jsonStr) ? null : RegionResp(jsonStr);
 
   RegionResp.fromJson(jsonRes) {
     code = jsonRes['code'];
@@ -25,11 +26,13 @@ class RegionResp {
   String toString() {
     return '{"code": $code, "ttl": $ttl, "message": ${message != null ? '${json.encode(message)}' : 'null'}, "data": $data}';
   }
+
+  String toJSON() => this.toString();
 }
 
 class Data {
-  List<Arch> archives;
-  Page page;
+  List<Arch?>? archives;
+  Page? page;
 
   Data.fromParams({this.archives, this.page});
 
@@ -37,7 +40,7 @@ class Data {
     archives = jsonRes['archives'] == null ? null : [];
 
     for (var archivesItem in archives == null ? [] : jsonRes['archives']) {
-      archives.add(archivesItem == null ? null : Arch.fromJson(archivesItem));
+      archives!.add(archivesItem == null ? null : Arch.fromJson(archivesItem));
     }
 
     page = jsonRes['page'] == null ? null : Page.fromJson(jsonRes['page']);
@@ -47,12 +50,14 @@ class Data {
   String toString() {
     return '{"archives": $archives, "page": $page}';
   }
+
+  String toJSON() => this.toString();
 }
 
 class Page {
-  int count;
-  int num;
-  int size;
+  int? count;
+  int? num;
+  int? size;
 
   Page.fromParams({this.count, this.num, this.size});
 
@@ -66,26 +71,28 @@ class Page {
   String toString() {
     return '{"count": $count, "num": $num, "size": $size}';
   }
+
+  String toJSON() => this.toString();
 }
 
 class Arch {
-  int aid;
-  int attribute;
-  int copyright;
-  int ctime;
-  int duration;
-  int pubdate;
-  int state;
-  int tid;
-  int videos;
-  String desc;
-  String dynamic;
-  String pic;
-  String title;
-  String tname;
-  Owner owner;
-  Right rights;
-  Stat stat;
+  int? aid;
+  int? attribute;
+  int? copyright;
+  int? ctime;
+  int? duration;
+  int? pubdate;
+  int? state;
+  int? tid;
+  int? videos;
+  String? desc;
+  String? dynamic;
+  String? pic;
+  String? title;
+  String? tname;
+  Owner? owner;
+  Right? rights;
+  Stat? stat;
 
   Arch.fromParams(
       {this.aid,
@@ -131,19 +138,21 @@ class Arch {
   String toString() {
     return '{"aid": $aid, "attribute": $attribute, "copyright": $copyright, "ctime": $ctime, "duration": $duration, "pubdate": $pubdate, "state": $state, "tid": $tid, "videos": $videos, "desc": ${desc != null ? '${json.encode(desc)}' : 'null'}, "dynamic": ${dynamic != null ? '${json.encode(dynamic)}' : 'null'}, "pic": ${pic != null ? '${json.encode(pic)}' : 'null'}, "title": ${title != null ? '${json.encode(title)}' : 'null'}, "tname": ${tname != null ? '${json.encode(tname)}' : 'null'}, "owner": $owner, "rights": $rights, "stat": $stat}';
   }
+
+  String toJSON() => this.toString();
 }
 
 class Stat {
-  int aid;
-  int coin;
-  int danmaku;
-  int favorite;
-  int his_rank;
-  int like;
-  int now_rank;
-  int reply;
-  int share;
-  int view;
+  int? aid;
+  int? coin;
+  int? danmaku;
+  int? favorite;
+  int? his_rank;
+  int? like;
+  int? now_rank;
+  int? reply;
+  int? share;
+  int? view;
 
   Stat.fromParams(
       {this.aid,
@@ -174,16 +183,18 @@ class Stat {
   String toString() {
     return '{"aid": $aid, "coin": $coin, "danmaku": $danmaku, "favorite": $favorite, "his_rank": $his_rank, "like": $like, "now_rank": $now_rank, "reply": $reply, "share": $share, "view": $view}';
   }
+
+  String toJSON() => this.toString();
 }
 
 class Right {
-  int bp;
-  int download;
-  int elec;
-  int hd5;
-  int movie;
-  int no_reprint;
-  int pay;
+  int? bp;
+  int? download;
+  int? elec;
+  int? hd5;
+  int? movie;
+  int? no_reprint;
+  int? pay;
 
   Right.fromParams(
       {this.bp,
@@ -208,12 +219,14 @@ class Right {
   String toString() {
     return '{"bp": $bp, "download": $download, "elec": $elec, "hd5": $hd5, "movie": $movie, "no_reprint": $no_reprint, "pay": $pay}';
   }
+
+  String toJSON() => this.toString();
 }
 
 class Owner {
-  int mid;
-  String face;
-  String name;
+  int? mid;
+  String? face;
+  String? name;
 
   Owner.fromParams({this.mid, this.face, this.name});
 
@@ -227,4 +240,6 @@ class Owner {
   String toString() {
     return '{"mid": $mid, "face": ${face != null ? '${json.encode(face)}' : 'null'}, "name": ${name != null ? '${json.encode(name)}' : 'null'}}';
   }
+
+  String toJSON() => this.toString();
 }
diff --git a/Test/WanResp.dart b/Test/WanResp.dart
index 0fe81f9..86b29fd 100644
--- a/Test/WanResp.dart
+++ b/Test/WanResp.dart
@@ -1,17 +1,18 @@
 import 'dart:convert' show json;
 
 class WanResp {
-  int errorCode;
-  String errorMsg;
-  List<Data> data;
+  int? errorCode;
+  String? errorMsg;
+  List<Data?>? data;
 
   WanResp.fromParams({this.errorCode, this.errorMsg, this.data});
 
-  factory WanResp(jsonStr) => jsonStr == null
-      ? null
-      : jsonStr is String
-          ? WanResp.fromJson(json.decode(jsonStr))
-          : WanResp.fromJson(jsonStr);
+  factory WanResp(Object jsonStr) => jsonStr is String
+      ? WanResp.fromJson(json.decode(jsonStr))
+      : WanResp.fromJson(jsonStr);
+
+  static WanResp? parse(jsonStr) =>
+      ['null', '', null].contains(jsonStr) ? null : WanResp(jsonStr);
 
   WanResp.fromJson(jsonRes) {
     errorCode = jsonRes['errorCode'];
@@ -19,7 +20,7 @@ class WanResp {
     data = jsonRes['data'] == null ? null : [];
 
     for (var dataItem in data == null ? [] : jsonRes['data']) {
-      data.add(dataItem == null ? null : Data.fromJson(dataItem));
+      data!.add(dataItem == null ? null : Data.fromJson(dataItem));
     }
   }
 
@@ -27,16 +28,18 @@ class WanResp {
   String toString() {
     return '{"errorCode": $errorCode, "errorMsg": ${errorMsg != null ? '${json.encode(errorMsg)}' : 'null'}, "data": $data}';
   }
+
+  String toJSON() => this.toString();
 }
 
 class Data {
-  int courseId;
-  int id;
-  int order;
-  int parentChapterId;
-  int visible;
-  String name;
-  List<Children> children;
+  int? courseId;
+  int? id;
+  int? order;
+  int? parentChapterId;
+  int? visible;
+  String? name;
+  List<Children?>? children;
 
   Data.fromParams(
       {this.courseId,
@@ -57,7 +60,7 @@ class Data {
     children = jsonRes['children'] == null ? null : [];
 
     for (var childrenItem in children == null ? [] : jsonRes['children']) {
-      children
+      children!
           .add(childrenItem == null ? null : Children.fromJson(childrenItem));
     }
   }
@@ -66,16 +69,18 @@ class Data {
   String toString() {
     return '{"courseId": $courseId, "id": $id, "order": $order, "parentChapterId": $parentChapterId, "visible": $visible, "name": ${name != null ? '${json.encode(name)}' : 'null'}, "children": $children}';
   }
+
+  String toJSON() => this.toString();
 }
 
 class Children {
-  int courseId;
-  int id;
-  int order;
-  int parentChapterId;
-  int visible;
-  String name;
-  List<dynamic> children;
+  int? courseId;
+  int? id;
+  int? order;
+  int? parentChapterId;
+  int? visible;
+  String? name;
+  List<dynamic?>? children;
 
   Children.fromParams(
       {this.courseId,
@@ -96,7 +101,7 @@ class Children {
     children = jsonRes['children'] == null ? null : [];
 
     for (var childrenItem in children == null ? [] : jsonRes['children']) {
-      children.add(childrenItem);
+      children!.add(childrenItem);
     }
   }
 
@@ -104,4 +109,6 @@ class Children {
   String toString() {
     return '{"courseId": $courseId, "id": $id, "order": $order, "parentChapterId": $parentChapterId, "visible": $visible, "name": ${name != null ? '${json.encode(name)}' : 'null'}, "children": $children}';
   }
+
+  String toJSON() => this.toString();
 }
diff --git a/Test/pubspec.yaml b/Test/pubspec.yaml
index 05066e6..a953fde 100644
--- a/Test/pubspec.yaml
+++ b/Test/pubspec.yaml
@@ -1,5 +1,8 @@
 name: Test
 description: Test
 
-dependencies:
-  test: "^1.2.0"
+environment:
+  sdk: '>=2.12.0 <3.0.0'
+
+dev_dependencies:
+  test: ^1.16.5
diff --git a/Test/test.dart b/Test/test.dart
index 155a70e..e2b858e 100644
--- a/Test/test.dart
+++ b/Test/test.dart
@@ -11,23 +11,22 @@ import 'ListTopResp.dart';
 import 'ListWithStringResp.dart';
 
 void main() {
-
-  test('Test null', (){
+  test('Test null', () {
     String str0 = '{"asd":[[[1]]],"qwe":[[[{"zxc":1}]]],"qaz":[1]}';
-    String str1 = '{"asd":[[[null,null]]],"qwe":[[[null]]],"qaz":[null,null,null]}';
+    String str1 =
+        '{"asd":[[[null,null]]],"qwe":[[[null]]],"qaz":[null,null,null]}';
     String str2 = '{"asd":[[[]]],"qwe":[[[{"zxc":null}]]],"qaz":[null]}';
     String str3 = '{"asd":[[]],"qwe":[[[]]],"qaz":null}';
     String str4 = '{"asd":[],"qwe":[[]],"qaz":null}';
     String str5 = '{"asd":null,"qwe":[],"qaz":null}';
-    String str6;
+    String? str6;
     expect(json.decode(new ListsResp(str0).toString()), json.decode(str0));
     expect(json.decode(new ListsResp(str1).toString()), json.decode(str1));
     expect(json.decode(new ListsResp(str2).toString()), json.decode(str2));
     expect(json.decode(new ListsResp(str3).toString()), json.decode(str3));
     expect(json.decode(new ListsResp(str4).toString()), json.decode(str4));
     expect(json.decode(new ListsResp(str5).toString()), json.decode(str5));
-    expect(json.decode(new ListsResp(str6).toString()), null);
-
+    expect(ListsResp.parse(str6), null);
   });
   test('Test Region', () {
     String str = readFromFile('Region');
@@ -41,80 +40,80 @@ void main() {
     expect(resp.code, jsonRes['code']);
     expect(resp.message, jsonRes['message']);
     expect(resp.ttl, jsonRes['ttl']);
-    expect(resp.data.page.num, jsonRes['data']['page']['num']);
-    expect(resp.data.page.size, jsonRes['data']['page']['size']);
-    expect(resp.data.page.count, jsonRes['data']['page']['count']);
+    expect(resp.data!.page!.num, jsonRes['data']['page']['num']);
+    expect(resp.data!.page!.size, jsonRes['data']['page']['size']);
+    expect(resp.data!.page!.count, jsonRes['data']['page']['count']);
     for (var index = 0; index < jsonRes['data']['archives'].length; index++) {
-      expect(resp.data.archives[index].aid,
+      expect(resp.data!.archives![index]!.aid,
           jsonRes['data']['archives'][index]['aid']);
-      expect(resp.data.archives[index].attribute,
+      expect(resp.data!.archives![index]!.attribute,
           jsonRes['data']['archives'][index]['attribute']);
-      expect(resp.data.archives[index].copyright,
+      expect(resp.data!.archives![index]!.copyright,
           jsonRes['data']['archives'][index]['copyright']);
-      expect(resp.data.archives[index].ctime,
+      expect(resp.data!.archives![index]!.ctime,
           jsonRes['data']['archives'][index]['ctime']);
-      expect(resp.data.archives[index].desc,
+      expect(resp.data!.archives![index]!.desc,
           jsonRes['data']['archives'][index]['desc']);
-      expect(resp.data.archives[index].duration,
+      expect(resp.data!.archives![index]!.duration,
           jsonRes['data']['archives'][index]['duration']);
-      expect(resp.data.archives[index].dynamic,
+      expect(resp.data!.archives![index]!.dynamic,
           jsonRes['data']['archives'][index]['dynamic']);
-      expect(resp.data.archives[index].pic,
+      expect(resp.data!.archives![index]!.pic,
           jsonRes['data']['archives'][index]['pic']);
-      expect(resp.data.archives[index].pubdate,
+      expect(resp.data!.archives![index]!.pubdate,
           jsonRes['data']['archives'][index]['pubdate']);
-      expect(resp.data.archives[index].state,
+      expect(resp.data!.archives![index]!.state,
           jsonRes['data']['archives'][index]['state']);
-      expect(resp.data.archives[index].tid,
+      expect(resp.data!.archives![index]!.tid,
           jsonRes['data']['archives'][index]['tid']);
-      expect(resp.data.archives[index].title,
+      expect(resp.data!.archives![index]!.title,
           jsonRes['data']['archives'][index]['title']);
-      expect(resp.data.archives[index].tname,
+      expect(resp.data!.archives![index]!.tname,
           jsonRes['data']['archives'][index]['tname']);
-      expect(resp.data.archives[index].videos,
+      expect(resp.data!.archives![index]!.videos,
           jsonRes['data']['archives'][index]['videos']);
 
-      expect(resp.data.archives[index].rights.bp,
+      expect(resp.data!.archives![index]!.rights!.bp,
           jsonRes['data']['archives'][index]['rights']['bp']);
-      expect(resp.data.archives[index].rights.download,
+      expect(resp.data!.archives![index]!.rights!.download,
           jsonRes['data']['archives'][index]['rights']['download']);
-      expect(resp.data.archives[index].rights.elec,
+      expect(resp.data!.archives![index]!.rights!.elec,
           jsonRes['data']['archives'][index]['rights']['elec']);
-      expect(resp.data.archives[index].rights.hd5,
+      expect(resp.data!.archives![index]!.rights!.hd5,
           jsonRes['data']['archives'][index]['rights']['hd5']);
-      expect(resp.data.archives[index].rights.movie,
+      expect(resp.data!.archives![index]!.rights!.movie,
           jsonRes['data']['archives'][index]['rights']['movie']);
-      expect(resp.data.archives[index].rights.no_reprint,
+      expect(resp.data!.archives![index]!.rights!.no_reprint,
           jsonRes['data']['archives'][index]['rights']['no_reprint']);
-      expect(resp.data.archives[index].rights.pay,
+      expect(resp.data!.archives![index]!.rights!.pay,
           jsonRes['data']['archives'][index]['rights']['pay']);
 
-      expect(resp.data.archives[index].owner.face,
+      expect(resp.data!.archives![index]!.owner!.face,
           jsonRes['data']['archives'][index]['owner']['face']);
-      expect(resp.data.archives[index].owner.mid,
+      expect(resp.data!.archives![index]!.owner!.mid,
           jsonRes['data']['archives'][index]['owner']['mid']);
-      expect(resp.data.archives[index].owner.name,
+      expect(resp.data!.archives![index]!.owner!.name,
           jsonRes['data']['archives'][index]['owner']['name']);
 
-      expect(resp.data.archives[index].stat.aid,
+      expect(resp.data!.archives![index]!.stat!.aid,
           jsonRes['data']['archives'][index]['stat']['aid']);
-      expect(resp.data.archives[index].stat.coin,
+      expect(resp.data!.archives![index]!.stat!.coin,
           jsonRes['data']['archives'][index]['stat']['coin']);
-      expect(resp.data.archives[index].stat.danmaku,
+      expect(resp.data!.archives![index]!.stat!.danmaku,
           jsonRes['data']['archives'][index]['stat']['danmaku']);
-      expect(resp.data.archives[index].stat.favorite,
+      expect(resp.data!.archives![index]!.stat!.favorite,
           jsonRes['data']['archives'][index]['stat']['favorite']);
-      expect(resp.data.archives[index].stat.his_rank,
+      expect(resp.data!.archives![index]!.stat!.his_rank,
           jsonRes['data']['archives'][index]['stat']['his_rank']);
-      expect(resp.data.archives[index].stat.like,
+      expect(resp.data!.archives![index]!.stat!.like,
           jsonRes['data']['archives'][index]['stat']['like']);
-      expect(resp.data.archives[index].stat.now_rank,
+      expect(resp.data!.archives![index]!.stat!.now_rank,
           jsonRes['data']['archives'][index]['stat']['now_rank']);
-      expect(resp.data.archives[index].stat.reply,
+      expect(resp.data!.archives![index]!.stat!.reply,
           jsonRes['data']['archives'][index]['stat']['reply']);
-      expect(resp.data.archives[index].stat.share,
+      expect(resp.data!.archives![index]!.stat!.share,
           jsonRes['data']['archives'][index]['stat']['share']);
-      expect(resp.data.archives[index].stat.view,
+      expect(resp.data!.archives![index]!.stat!.view,
           jsonRes['data']['archives'][index]['stat']['view']);
     }
 
@@ -135,30 +134,30 @@ void main() {
     expect(resp.errorMsg, jsonRes['errorMsg']);
 
     for (var index = 0; index < jsonRes['data'].length; index++) {
-      expect(resp.data[index].name, jsonRes['data'][index]['name']);
-      expect(resp.data[index].courseId, jsonRes['data'][index]['courseId']);
-      expect(resp.data[index].id, jsonRes['data'][index]['id']);
-      expect(resp.data[index].order, jsonRes['data'][index]['order']);
-      expect(resp.data[index].parentChapterId,
+      expect(resp.data![index]!.name, jsonRes['data'][index]['name']);
+      expect(resp.data![index]!.courseId, jsonRes['data'][index]['courseId']);
+      expect(resp.data![index]!.id, jsonRes['data'][index]['id']);
+      expect(resp.data![index]!.order, jsonRes['data'][index]['order']);
+      expect(resp.data![index]!.parentChapterId,
           jsonRes['data'][index]['parentChapterId']);
-      expect(resp.data[index].visible, jsonRes['data'][index]['visible']);
+      expect(resp.data![index]!.visible, jsonRes['data'][index]['visible']);
 
       for (var cindex = 0;
           cindex < jsonRes['data'][index]['children'].length;
           cindex++) {
-        expect(resp.data[index].children[cindex].children,
+        expect(resp.data![index]!.children![cindex]!.children,
             jsonRes['data'][index]['children'][cindex]['children']);
-        expect(resp.data[index].children[cindex].visible,
+        expect(resp.data![index]!.children![cindex]!.visible,
             jsonRes['data'][index]['children'][cindex]['visible']);
-        expect(resp.data[index].children[cindex].parentChapterId,
+        expect(resp.data![index]!.children![cindex]!.parentChapterId,
             jsonRes['data'][index]['children'][cindex]['parentChapterId']);
-        expect(resp.data[index].children[cindex].order,
+        expect(resp.data![index]!.children![cindex]!.order,
             jsonRes['data'][index]['children'][cindex]['order']);
-        expect(resp.data[index].children[cindex].courseId,
+        expect(resp.data![index]!.children![cindex]!.courseId,
             jsonRes['data'][index]['children'][cindex]['courseId']);
-        expect(resp.data[index].children[cindex].name,
+        expect(resp.data![index]!.children![cindex]!.name,
             jsonRes['data'][index]['children'][cindex]['name']);
-        expect(resp.data[index].children[cindex].id,
+        expect(resp.data![index]!.children![cindex]!.id,
             jsonRes['data'][index]['children'][cindex]['id']);
       }
 
@@ -168,7 +167,6 @@ void main() {
   });
 
   test('test many empty', () {
-
     String str = readFromFile('Empty');
     EmptyResp resp = new EmptyResp(str);
     var jsonRes = json.decode(str);
@@ -177,17 +175,15 @@ void main() {
     expect(resp.toString(), new EmptyResp(jsonRes).toString());
 
     /// 逐个字段检查是否与json.decode()的结果相同
-    expect(resp.qwe.asd, jsonRes['qwe']['asd']);
-    expect(resp.qwe.zxc, jsonRes['qwe']['zxc']);
-    expect(resp.qwe.qaz, jsonRes['qwe']['qaz']);
+    expect(resp.qwe!.asd, jsonRes['qwe']['asd']);
+    expect(resp.qwe!.zxc, jsonRes['qwe']['zxc']);
+    expect(resp.qwe!.qaz, jsonRes['qwe']['qaz']);
 
     /// 检查bean对象toString还原成json字符串后再交给json解析的结果是否与原始字符串相同
     expect(jsonRes, json.decode(resp.toString()));
   });
 
-
   test('test fucking lists', () {
-
     String str = readFromFile('Lists');
     ListsResp resp = new ListsResp(str);
     var jsonRes = json.decode(str);
@@ -196,16 +192,15 @@ void main() {
     expect(resp.toString(), new ListsResp(jsonRes).toString());
 
     /// 逐个字段检查是否与json.decode()的结果相同
-    expect(resp.asd[0][0][0], jsonRes['asd'][0][0][0]);
-    expect(resp.qwe[0][0][0].zxc, jsonRes['qwe'][0][0][0]['zxc']);
+    expect(resp.asd![0]![0]![0], jsonRes['asd'][0][0][0]);
+    expect(resp.qwe![0]![0]![0]!.zxc, jsonRes['qwe'][0][0][0]['zxc']);
     expect(resp.qaz, jsonRes['qaz']);
 
     /// 检查bean对象toString还原成json字符串后再交给json解析的结果是否与原始字符串相同
     expect(jsonRes, json.decode(resp.toString()));
-});
+  });
 
   test('test ignore map', () {
-
     String str = readFromFile('IgnoreMap');
     IgnoreMapResp resp = new IgnoreMapResp(str);
     var jsonRes = json.decode(str);
@@ -214,15 +209,15 @@ void main() {
     expect(resp.toString(), new IgnoreMapResp(jsonRes).toString());
 
     /// 逐个字段检查是否与json.decode()的结果相同
-    expect(resp.data.wc, jsonRes['data']['wc']);
-    expect(resp.data.author, jsonRes['data']['author']);
-    expect(resp.data.content, jsonRes['data']['content']);
-    expect(resp.data.digest, jsonRes['data']['digest']);
-    expect(resp.data.title, jsonRes['data']['title']);
-    expect(resp.data.extra.a, jsonRes['data']['extra']['a']);
-    expect(resp.data.extra.b, jsonRes['data']['extra']['b']);
-    expect(resp.data.extra.c, jsonRes['data']['extra']['c']);
-    expect(resp.data.date, jsonRes['data']['date']);
+    expect(resp.data!.wc, jsonRes['data']['wc']);
+    expect(resp.data!.author, jsonRes['data']['author']);
+    expect(resp.data!.content, jsonRes['data']['content']);
+    expect(resp.data!.digest, jsonRes['data']['digest']);
+    expect(resp.data!.title, jsonRes['data']['title']);
+    expect(resp.data!.extra!.a, jsonRes['data']['extra']['a']);
+    expect(resp.data!.extra!.b, jsonRes['data']['extra']['b']);
+    expect(resp.data!.extra!.c, jsonRes['data']['extra']['c']);
+    expect(resp.data!.date, jsonRes['data']['date']);
 
     /// 检查bean对象toString还原成json字符串后再交给json解析的结果是否与原始字符串相同
     expect(jsonRes, json.decode(resp.toString()));
@@ -233,9 +228,11 @@ void main() {
     ListTopResp resp = ListTopResp(str);
 
     var jsonRes = json.decode(str);
+
     /// 测试传入String和json进行解析的结果是否相同
     expect(resp.toString(), new ListTopResp(jsonRes).toString());
-    expect(resp.list.toString().replaceAll(' ', ''), json.encode(jsonRes).replaceAll('\n', '').replaceAll(' ', ''));
+    expect(resp.list.toString().replaceAll(' ', ''),
+        json.encode(jsonRes).replaceAll('\n', '').replaceAll(' ', ''));
   });
 
   test('test list with string', () {
@@ -243,18 +240,19 @@ void main() {
     ListWithStringResp resp = ListWithStringResp(str);
 
     var jsonRes = json.decode(str);
+
     /// 测试传入String和json进行解析的结果是否相同
     expect(resp.toString(), new ListWithStringResp(jsonRes).toString());
-    expect(resp.toString().replaceAll(' ', ''), json.encode(jsonRes).replaceAll('\n', '').replaceAll(' ', ''));
+    expect(resp.toString().replaceAll(' ', ''),
+        json.encode(jsonRes).replaceAll('\n', '').replaceAll(' ', ''));
   });
-
 }
 
 String readFromFile(String name) {
   String str = new File('${name}Test.json').readAsStringSync();
   int index1 = str.indexOf('{');
   int index2 = str.indexOf('[');
-  index1 = index1 == -1 ? 0: index1;
-  index2 = index2 == -1 ? 0: index2;
+  index1 = index1 == -1 ? 0 : index1;
+  index2 = index2 == -1 ? 0 : index2;
   return str.substring(min(index1, index2));
 }
diff --git a/Test/test.sh b/Test/test.sh
index f893920..3d00459 100644
--- a/Test/test.sh
+++ b/Test/test.sh
@@ -5,4 +5,4 @@ env PUB_ALLOW_PRERELEASE_SDK=quiet $(echo $(which flutter) | awk '{print substr(
 
 # 运行测试
 echo test start...
-$(echo $(which flutter) | awk '{print substr($0,0,length()-7)}')cache/dart-sdk/bin/dart --preview-dart-2 --null_safety test.dart
\ No newline at end of file
+$(echo $(which flutter) | awk '{print substr($0,0,length()-7)}')cache/dart-sdk/bin/dart test.dart
diff --git a/check_version.py b/check_version.py
index 694c5fd..6f3c9e4 100644
--- a/check_version.py
+++ b/check_version.py
@@ -16,7 +16,7 @@
 from PyQt5.QtWidgets import QMessageBox
 from tools import msg_box_ui
 
-code = 0.8
+code = 0.9
 ignore_code = 0.0
 
 check_last_version_thread = None
diff --git a/formatter.py b/formatter.py
index 30e8748..9d46412 100644
--- a/formatter.py
+++ b/formatter.py
@@ -284,5 +284,5 @@ def custom_ui():
     custom_ui()
     widget.show()
     code = check_version()
-    widget.setWindowTitle(widget.windowTitle().replace('code', str(code)))
+    widget.setWindowTitle(widget.windowTitle().replace('code', str(code) + '-nullsafety'))
     sys.exit(app.exec_())
diff --git a/template_code.py b/template_code.py
index bb00e1d..b254bbd 100644
--- a/template_code.py
+++ b/template_code.py
@@ -21,6 +21,8 @@ class ${type} {
   String toString() {
     return '{${toString}}';
   }
+  
+  String toJson() => this.toString();
 }
 
 """
@@ -29,7 +31,7 @@ class ${type} {
   ${list_count}${class_type}${>count} ${name}${current_child} = ${name}${parent_items} == null ? null : [];
     for (var ${name}${current_items} in ${name}${current_child} == null ? [] : ${name}${parent_items}){
       ${loop}
-      ${name}${current_child}.add(${name}${child_child});
+      ${name}${current_child}!.add(${name}${child_child});
     }
 """
 
diff --git a/tools.py b/tools.py
index 6366ece..f5f7715 100644
--- a/tools.py
+++ b/tools.py
@@ -57,7 +57,7 @@ def check_level_type(t):
 
 def list_code_loop(code, count, total, n, ct):
     list_count = 'List<' * (total - count)
-    ab_count = '>' * (total - count)
+    ab_count = '?>' * (total - count) + '?'
 
     current_child = 'Child' * count
     child_child = 'Child' * (count + 1)
@@ -75,7 +75,7 @@ def list_code_loop(code, count, total, n, ct):
 
 # 向代码模板中插入变量
 def build_list_construction(t, f, n):
-    class_type = t.replace('List<', '').replace('>', '')
+    class_type = t.replace('List<', '').replace('>', '').replace('?', '')
 
     list_loop = 'jsonRes[\'%s\'] == null ? null : [];\n' % f
     assert isinstance(t, str)
@@ -102,7 +102,7 @@ def add_param_to_code(code, param):
     (f, t, n) = param
 
     # 先按照基本数据类型方式处理
-    properties = '  %s %s;\n' % (t, n)
+    properties = '  %s? %s;\n' % (t, n)
     this_properties = 'this.%s, ' % n
     construction = '    %s = jsonRes[\'%s\'];\n' % (n, f)
     to_string = '"%s": $%s, ' % (f, n)
@@ -122,7 +122,7 @@ def add_param_to_code(code, param):
     t_code = check_level_type(t)
 
     # 字符串类型、List<String>类型和Map类型处理,需要修改toString中的输出方式
-    if t_code in [0, 2] or 'List<String>' in t:
+    if t_code in [0, 2] or 'List<String?>' in t:
         code = code.replace(': $%s' % n, ': ${%s != null?\'${json.encode(%s)}\':\'null\'}' % (n, n))
 
     # dict类型处理，只需要修改construction中的输出方式
@@ -174,6 +174,9 @@ def build_level_code(level_bean):
                         child_bean.append(level_bean.pop(0))
                     build_level_code(child_bean)
 
+                if t != 'List<>':
+                    t = t.replace('>', '?>')
+
             # 不管如何，到这里的数据都是目前dict的一级子数据，作为参数传入模板中
             code = add_param_to_code(code, (f, t, n))
         codes.append(code.replace(', ${toString}', '').replace('${construction}', '').replace('${properties}', '').replace('${this.properties}', ''))
@@ -205,7 +208,7 @@ def generate_code(work_bean):
         res = res.replace('jsonRes[\'json_list\']', 'jsonRes', 2)
 
     # 如果json中存在空list这种操蛋情况，将list类型从list<>修改成list<dynamic>
-    res = res.replace('List<>', 'List<dynamic>')
+    res = res.replace('List<>', 'List<dynamic?>')
 
     # 移除参数构造函数用模板生成后多余的逗号和空格
     res = res.replace(', });', '});')
@@ -225,9 +228,10 @@ def generate_code(work_bean):
         out_res += (line + '\n')
         if first and r'.fromParams({this.' in line:
             class_name = line.split(r'.fromParams({this.')[0].strip()
-            out_res += '\n  factory %s(jsonStr) => [\'null\', \'\', null].contains(jsonStr) ? null : ' \
-                       'jsonStr is String ? %s.fromJson(json.decode(jsonStr)) : %s.fromJson(jsonStr);\n' \
+            out_res += '\n  factory %s(Object jsonStr) => jsonStr is String ? %s.fromJson(json.decode(jsonStr)) : %s.fromJson(jsonStr);\n' \
                        % (class_name, class_name, class_name)
+            out_res += '\n  static %s? parse(jsonStr) => [\'null\', \'\', null].contains(jsonStr) ? null : %s(jsonStr);\n' \
+                       % (class_name, class_name)
             first = False
     return out_res
 
diff --git a/version b/version
index f726831..9bf5bf5 100644
--- a/version
+++ b/version
@@ -1,4 +1,4 @@
 {
-  "code": 0.7,
-  "desc": "1.可以通过下拉框将对象类型设置为Map<String, dynamic>来避免该对象字段的解析，参考issue #13\n2.点击Name栏使字段转为驼峰 & 解析List的时候读取多个元素，参考issue #17\n3.修复闪退崩溃issue #23"
+  "code": 0.9,
+  "desc": "迁移至空安全语法。"
 }