diff --git a/lib/http_proxy.dart b/lib/http_proxy.dart
index 80fe7c5..45ece77 100644
--- a/lib/http_proxy.dart
+++ b/lib/http_proxy.dart
@@ -3,17 +3,17 @@ import 'package:flutter/services.dart';
 
 MethodChannel _channel = MethodChannel('com.lm.http.proxy');
 
-Future<String> _getProxyHost() async {
+Future<String?> _getProxyHost() async {
   return await _channel.invokeMethod('getProxyHost');
 }
 
-Future<String> _getProxyPort() async {
+Future<String?> _getProxyPort() async {
   return await _channel.invokeMethod('getProxyPort');
 }
 
 class HttpProxy extends HttpOverrides {
-  String host;
-  String port;
+  String? host;
+  String? port;
 
   HttpProxy._(this.host, this.port);
 
@@ -22,7 +22,7 @@ class HttpProxy extends HttpOverrides {
   }
 
   @override
-  HttpClient createHttpClient(SecurityContext context) {
+  HttpClient createHttpClient(SecurityContext? context) {
     var client = super.createHttpClient(context);
     client.badCertificateCallback =
         (X509Certificate cert, String host, int port) {
@@ -32,7 +32,7 @@ class HttpProxy extends HttpOverrides {
   }
 
   @override
-  String findProxyFromEnvironment(Uri url, Map<String, String> environment) {
+  String findProxyFromEnvironment(Uri url, Map<String, String>? environment) {
     if (host == null) {
       return super.findProxyFromEnvironment(url, environment);
     }
diff --git a/pubspec.yaml b/pubspec.yaml
index 5f25653..05dee28 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -5,13 +5,13 @@ homepage: https://github.com/wslaimin
 repository: https://github.com/wslaimin/http_proxy
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
   flutter: ">=1.10.0"
 
 dependencies:
   flutter:
     sdk: flutter
-  http: ^0.12.1
+  http: ^0.13.1
 
 dev_dependencies:
   flutter_test: