diff --git a/CHANGELOG.md b/CHANGELOG.md
index eac26e6..c88d6f3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # CHANGELOG
 
+## [1.0.0-nullsafety.0]
+
+* migrate to sound null safety.
+
 ## [0.1.3]
 
 * listenable value.
diff --git a/example/pubspec.lock b/example/pubspec.lock
index 88db764..11018f7 100644
--- a/example/pubspec.lock
+++ b/example/pubspec.lock
@@ -5,84 +5,84 @@ packages:
     dependency: transitive
     description:
       name: async
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "2.5.0"
   auto_size_text:
     dependency: transitive
     description:
       name: auto_size_text
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "3.0.0-nullsafety.0"
   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"
   characters:
     dependency: transitive
     description:
       name: characters
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "1.1.0"
   charcode:
     dependency: transitive
     description:
       name: charcode
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "1.2.0"
   clock:
     dependency: transitive
     description:
       name: clock
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "1.1.0"
   collection:
     dependency: transitive
     description:
       name: collection
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "1.15.0"
   cupertino_icons:
     dependency: "direct main"
     description:
       name: cupertino_icons
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.0"
+    version: "1.0.2"
   device_info:
     dependency: transitive
     description:
       name: device_info
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "2.0.0"
   device_info_platform_interface:
     dependency: transitive
     description:
       name: device_info_platform_interface
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "2.0.1"
   dio:
     dependency: "direct main"
     description:
       name: dio
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "4.0.0-prev3"
   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"
   flutter:
@@ -94,7 +94,7 @@ packages:
     dependency: transitive
     description:
       name: flutter_highlight
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "0.7.0"
   flutter_test:
@@ -106,56 +106,56 @@ packages:
     dependency: "direct main"
     description:
       name: get
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
-    version: "3.24.0"
+    version: "3.26.0"
   highlight:
     dependency: transitive
     description:
       name: highlight
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "0.7.0"
   http_parser:
     dependency: transitive
     description:
       name: http_parser
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "4.0.0"
   matcher:
     dependency: transitive
     description:
       name: matcher
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "0.12.10"
   meta:
     dependency: transitive
     description:
       name: meta
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "1.3.0"
   package_info:
     dependency: transitive
     description:
       name: package_info
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "2.0.0"
   path:
     dependency: transitive
     description:
       name: path
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "1.8.0"
   plugin_platform_interface:
     dependency: transitive
     description:
       name: plugin_platform_interface
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "2.0.0"
   power_logger:
@@ -174,56 +174,56 @@ packages:
     dependency: transitive
     description:
       name: source_span
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "1.8.0"
   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"
   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"
   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"
   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"
   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"
   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"
   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"
 sdks:
diff --git a/pubspec.lock b/pubspec.lock
index 249c799..b178bf8 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -5,77 +5,77 @@ packages:
     dependency: transitive
     description:
       name: async
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "2.5.0"
   auto_size_text:
     dependency: "direct main"
     description:
       name: auto_size_text
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "3.0.0-nullsafety.0"
   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"
   characters:
     dependency: transitive
     description:
       name: characters
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "1.1.0"
   charcode:
     dependency: transitive
     description:
       name: charcode
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "1.2.0"
   clock:
     dependency: transitive
     description:
       name: clock
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "1.1.0"
   collection:
     dependency: transitive
     description:
       name: collection
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "1.15.0"
   device_info:
     dependency: "direct main"
     description:
       name: device_info
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "2.0.0"
   device_info_platform_interface:
     dependency: transitive
     description:
       name: device_info_platform_interface
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "2.0.1"
   dio:
     dependency: "direct main"
     description:
       name: dio
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "4.0.0-prev3"
   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"
   flutter:
@@ -87,7 +87,7 @@ packages:
     dependency: "direct main"
     description:
       name: flutter_highlight
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "0.7.0"
   flutter_test:
@@ -99,49 +99,49 @@ packages:
     dependency: transitive
     description:
       name: highlight
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "0.7.0"
   http_parser:
     dependency: transitive
     description:
       name: http_parser
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "4.0.0"
   matcher:
     dependency: transitive
     description:
       name: matcher
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "0.12.10"
   meta:
     dependency: transitive
     description:
       name: meta
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "1.3.0"
   package_info:
     dependency: "direct main"
     description:
       name: package_info
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "2.0.0"
   path:
     dependency: transitive
     description:
       name: path
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "1.8.0"
   plugin_platform_interface:
     dependency: transitive
     description:
       name: plugin_platform_interface
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "2.0.0"
   sky_engine:
@@ -153,56 +153,56 @@ packages:
     dependency: transitive
     description:
       name: source_span
-      url: "https://pub.flutter-io.cn"
+      url: "https://pub.dartlang.org"
     source: hosted
     version: "1.8.0"
   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"
   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"
   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"
   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"
   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"
   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"
   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"
 sdks: