diff --git a/.gitignore b/.gitignore
index 5a60f77..0f9779f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,6 +8,7 @@
 .buildlog/
 .history
 .svn/
+.fvm/
 
 # IntelliJ related
 *.iml
diff --git a/CHANGELOG.md b/CHANGELOG.md
index c9a7d65..43e1bc8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## [4.0.0-nullsafety] - Release Flags
+* support nullsafety
+* update flutter_svg packages to ^0.18.0
+
 ## [3.2.0] - Release Flags
 * Add Disputed territories. [PR39](https://github.com/LunaGao/flag_flutter/pull/39) by [markusgeert](https://github.com/markusgeert)
 
diff --git a/README.md b/README.md
index b256940..0c89a49 100644
--- a/README.md
+++ b/README.md
@@ -54,6 +54,7 @@ switch Flutter SDK channel
 flutter channel
 flutter channel <channel-name>
 ```
+Or using [fvm](https://github.com/leoafarias/fvm)
 * `develop` --> develop
 * `stable` --> verison X.Y.Z  (using latest `stable` channel Flutter SDK)
 ```
@@ -61,5 +62,10 @@ Channel stable, 1.22.5
 ```
 * `master` --> verison X.Y.Z-pre  (using latest `bate` channel Flutter SDK)
 ```
-Channel beta, 1.20.0-7.3.pre
+Channel beta, 1.25.0-8.2.pre
 ```
+
+## Upload to PUB
+
+* `flutter pub publish --dry-run`
+* `flutter pub publish`
\ No newline at end of file
diff --git a/pubspec.lock b/pubspec.lock
index d6bd28a..c6f4dbb 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -5,58 +5,58 @@ packages:
     dependency: transitive
     description:
       name: async
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.5.0-nullsafety.1"
+    version: "2.5.0-nullsafety.3"
   boolean_selector:
     dependency: transitive
     description:
       name: boolean_selector
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.0-nullsafety.1"
+    version: "2.1.0-nullsafety.3"
   characters:
     dependency: transitive
     description:
       name: characters
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.0-nullsafety.3"
+    version: "1.1.0-nullsafety.5"
   charcode:
     dependency: transitive
     description:
       name: charcode
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.2.0-nullsafety.1"
+    version: "1.2.0-nullsafety.3"
   clock:
     dependency: transitive
     description:
       name: clock
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.0-nullsafety.1"
+    version: "1.1.0-nullsafety.3"
   collection:
     dependency: transitive
     description:
       name: collection
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.15.0-nullsafety.3"
+    version: "1.15.0-nullsafety.5"
   convert:
     dependency: transitive
     description:
       name: convert
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "2.1.1"
   fake_async:
     dependency: transitive
     description:
       name: fake_async
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.2.0-nullsafety.1"
+    version: "1.2.0-nullsafety.3"
   flutter:
     dependency: "direct main"
     description: flutter
@@ -66,9 +66,9 @@ packages:
     dependency: "direct main"
     description:
       name: flutter_svg
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.19.1"
+    version: "0.19.2+1"
   flutter_test:
     dependency: "direct dev"
     description: flutter
@@ -78,42 +78,42 @@ packages:
     dependency: transitive
     description:
       name: matcher
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.12.10-nullsafety.1"
+    version: "0.12.10-nullsafety.3"
   meta:
     dependency: transitive
     description:
       name: meta
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.3.0-nullsafety.3"
+    version: "1.3.0-nullsafety.6"
   path:
     dependency: transitive
     description:
       name: path
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.8.0-nullsafety.1"
+    version: "1.8.0-nullsafety.3"
   path_drawing:
     dependency: transitive
     description:
       name: path_drawing
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "0.4.1+1"
   path_parsing:
     dependency: transitive
     description:
       name: path_parsing
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "0.1.4"
   petitparser:
     dependency: transitive
     description:
       name: petitparser
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "3.1.0"
   sky_engine:
@@ -125,65 +125,65 @@ packages:
     dependency: transitive
     description:
       name: source_span
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.8.0-nullsafety.2"
+    version: "1.8.0-nullsafety.4"
   stack_trace:
     dependency: transitive
     description:
       name: stack_trace
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.10.0-nullsafety.1"
+    version: "1.10.0-nullsafety.6"
   stream_channel:
     dependency: transitive
     description:
       name: stream_channel
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.0-nullsafety.1"
+    version: "2.1.0-nullsafety.3"
   string_scanner:
     dependency: transitive
     description:
       name: string_scanner
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.0-nullsafety.1"
+    version: "1.1.0-nullsafety.3"
   term_glyph:
     dependency: transitive
     description:
       name: term_glyph
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.2.0-nullsafety.1"
+    version: "1.2.0-nullsafety.3"
   test_api:
     dependency: transitive
     description:
       name: test_api
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.19-nullsafety.2"
+    version: "0.2.19-nullsafety.6"
   typed_data:
     dependency: transitive
     description:
       name: typed_data
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.3.0-nullsafety.3"
+    version: "1.3.0-nullsafety.5"
   vector_math:
     dependency: transitive
     description:
       name: vector_math
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.0-nullsafety.3"
+    version: "2.1.0-nullsafety.5"
   xml:
     dependency: transitive
     description:
       name: xml
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "4.5.1"
 sdks:
-  dart: ">=2.10.0-110 <2.11.0"
-  flutter: ">=1.18.0-6.0.pre <2.0.0"
+  dart: ">=2.12.0-0.0 <3.0.0"
+  flutter: ">=1.24.0-6.0.pre <2.0.0"
diff --git a/pubspec.yaml b/pubspec.yaml
index 8d75de5..adc403b 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,6 +1,6 @@
 name: flag
 description: A flag Flutter package. Use for showing flags. All flags came from https://www.un.org/en/member-states/index.html . 
-version: 3.2.0
+version: 4.0.0-nullsafety
 homepage: https://github.com/LunaGao/flag_flutter
 
 environment: