Update example and plugin. (#32)

* Update example to null safety, fix int? -> int for sendFilePayload

* Fixed example and plugin errors when running on sound null safety

example/.gitignore

@@ -15,56 +15,32 @@
 *.iws
 .idea/
 
-# Visual Studio Code related
-.vscode/
+# The .vscode folder contains launch configuration and tasks you configure in
+# VS Code which you may wish to be included in version control, so this line
+# is commented out by default.
+#.vscode/
 
 # Flutter/Dart/Pub related
 **/doc/api/
+**/ios/Flutter/.last_build_id
 .dart_tool/
 .flutter-plugins
+.flutter-plugins-dependencies
 .packages
 .pub-cache/
 .pub/
 /build/
 
-# Android related
-**/android/**/gradle-wrapper.jar
-**/android/.gradle
-**/android/captures/
-**/android/gradlew
-**/android/gradlew.bat
-**/android/local.properties
-**/android/**/GeneratedPluginRegistrant.java
+# Web related
+lib/generated_plugin_registrant.dart
 
-# iOS/XCode related
-**/ios/**/*.mode1v3
-**/ios/**/*.mode2v3
-**/ios/**/*.moved-aside
-**/ios/**/*.pbxuser
-**/ios/**/*.perspectivev3
-**/ios/**/*sync/
-**/ios/**/.sconsign.dblite
-**/ios/**/.tags*
-**/ios/**/.vagrant/
-**/ios/**/DerivedData/
-**/ios/**/Icon?
-**/ios/**/Pods/
-**/ios/**/.symlinks/
-**/ios/**/profile
-**/ios/**/xcuserdata
-**/ios/.generated/
-**/ios/Flutter/App.framework
-**/ios/Flutter/Flutter.framework
-**/ios/Flutter/Generated.xcconfig
-**/ios/Flutter/app.flx
-**/ios/Flutter/app.zip
-**/ios/Flutter/flutter_assets/
-**/ios/ServiceDefinitions.json
-**/ios/Runner/GeneratedPluginRegistrant.*
+# Symbolication related
+app.*.symbols
 
-# Exceptions to above rules.
-!**/ios/**/default.mode1v3
-!**/ios/**/default.mode2v3
-!**/ios/**/default.pbxuser
-!**/ios/**/default.perspectivev3
-!/packages/flutter_tools/test/data/dart_dependencies_test/**/.packages
+# Obfuscation related
+app.*.map.json
+
+# Android Studio will place build artifacts here
+/android/app/debug
+/android/app/profile
+/android/app/release