[connectivity] Clear networkCallback object as soon as stream is cancelled (#3303)

Set networkCallback back to null when event stream is cancelled
diff --git a/packages/connectivity/connectivity/CHANGELOG.md b/packages/connectivity/connectivity/CHANGELOG.md
index 60765d1..f215449 100644
--- a/packages/connectivity/connectivity/CHANGELOG.md
+++ b/packages/connectivity/connectivity/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 3.0.0-nullsafety.2
+
+* Android: Cleanup the NetworkCallback object when a connectivity stream is cancelled
+
 ## 3.0.0-nullsafety.1
 
 * Bump Dart SDK to support null safety.
diff --git a/packages/connectivity/connectivity/android/src/main/java/io/flutter/plugins/connectivity/ConnectivityBroadcastReceiver.java b/packages/connectivity/connectivity/android/src/main/java/io/flutter/plugins/connectivity/ConnectivityBroadcastReceiver.java
index ca3ccff..dbf96bd 100644
--- a/packages/connectivity/connectivity/android/src/main/java/io/flutter/plugins/connectivity/ConnectivityBroadcastReceiver.java
+++ b/packages/connectivity/connectivity/android/src/main/java/io/flutter/plugins/connectivity/ConnectivityBroadcastReceiver.java
@@ -64,6 +64,7 @@
     if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
       if (networkCallback != null) {
         connectivity.getConnectivityManager().unregisterNetworkCallback(networkCallback);
+        networkCallback = null;
       }
     } else {
       context.unregisterReceiver(this);
diff --git a/packages/connectivity/connectivity/pubspec.yaml b/packages/connectivity/connectivity/pubspec.yaml
index 2f6d781..916fa08 100644
--- a/packages/connectivity/connectivity/pubspec.yaml
+++ b/packages/connectivity/connectivity/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Flutter plugin for discovering the state of the network (WiFi &
   mobile/cellular) connectivity on Android and iOS.
 homepage: https://github.com/flutter/plugins/tree/master/packages/connectivity/connectivity
-version: 3.0.0-nullsafety.1
+version: 3.0.0-nullsafety.2
 
 flutter:
   plugin: