Fix example

Author: Lennart Martens

example/android/app/build.gradle

@@ -26,7 +26,7 @@ apply plugin: 'kotlin-android'
 apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
 
 android {
-    compileSdkVersion 30
+    compileSdkVersion 31
 
     sourceSets {
         main.java.srcDirs += 'src/main/kotlin'

example/android/build.gradle

@@ -1,5 +1,5 @@
 buildscript {
-    ext.kotlin_version = '1.3.50'
+    ext.kotlin_version = '1.6.10'
     repositories {
         google()
         mavenCentral()

example/lib/main.dart

@@ -31,14 +31,14 @@ class _MyAppState extends State<MyApp> {
     super.initState();
 
     /// [Authenticator] needs to be registered as an app lifecycle observer
-    WidgetsBinding.instance?.addObserver(globalAuthenticator);
+    WidgetsBinding.instance.addObserver(globalAuthenticator);
   }
 
   @override
   void dispose() {
     /// When disposing of the app, remove [Authenticator]'s subscription
     /// to lifecycle events
-    WidgetsBinding.instance?.removeObserver(globalAuthenticator);
+    WidgetsBinding.instance.removeObserver(globalAuthenticator);
     super.dispose();
   }