Android: Null is not a subtype of String in AndroidInAppWebViewController._handleMethod after upgrading to 6.2.0-beta.3

[changs97]

Is there an existing issue for this?

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Current Behavior

After upgrading from flutter_inappwebview 6.1.5 to flutter_inappwebview 6.2.0-beta.3, the Android app logs a runtime type error from AndroidInAppWebViewController._handleMethod.

The error occurs during normal WebView usage. I did not explicitly long-press the WebView content, and the app does not pass a custom ContextMenu to InAppWebView.

The stacktrace points to the plugin's Android MethodChannel event dispatcher:

type 'Null' is not a subtype of type 'String'
#0      AndroidInAppWebViewController._handleMethod (package:flutter_inappwebview_android/src/in_app_webview/in_app_webview_controller.dart:1412)
#1      InternalChannelController.initMethodCallHandler.<anonymous closure> (package:flutter_inappwebview_platform_interface/src/util.dart:631)
#2      MethodChannel._handleAsMethodCall (package:flutter/src/services/platform_channel.dart:607)
#3      MethodChannel.setMethodCallHandler.<anonymous closure> (package:flutter/src/services/platform_channel.dart:597)
#4      _DefaultBinaryMessenger.setMessageHandler.<anonymous closure> (package:flutter/src/services/binding.dart:663)
#5      _invoke2 (dart:ui/hooks.dart:455)
#6      _ChannelCallbackRecord.invoke (dart:ui/channel_buffers.dart:45)
#7      _Channel.push (dart:ui/channel_buffers.dart:136)
#8      ChannelBuffers.push (dart:ui/channel_buffers.dart:344)
#9      PlatformDispatcher._dispatchPlatformMessage (dart:ui/platform_dispatcher.dart:822)
#10     _dispatchPlatformMessage (dart:ui/hooks.dart:369)

This looks like a native-to-Dart MethodChannel payload nullability issue. The Android implementation appears to read some MethodChannel arguments as non-null String, but Android native can apparently send null in at least one path.

Expected Behavior

The plugin should not throw a Dart runtime type error when Android native sends a nullable value through MethodChannel.

If a native event argument can be null, the Dart side should either accept nullable values or guard before creating non-null String values.

For example:

final String? url = call.arguments["url"];
if (url == null) {
  break;
}

or, for optional display values:

final String title = call.arguments["title"] ?? "";

Steps with code example to reproduce

1. Use flutter_inappwebview: ^6.2.0-beta.3.
2. Run the app on Android.
3. Open a screen containing InAppWebView.
4. Navigate normally inside the WebView.
5. Observe the runtime error from AndroidInAppWebViewController._handleMethod.

The app creates InAppWebView without a custom ContextMenu:

InAppWebView(
  initialUrlRequest: initialUrlRequest,
  initialSettings: CommonUtils.getCommonWebSetting(userAgent),
)

Common settings include:

InAppWebViewSettings(
  disableContextMenu: true,
  disableLongPressContextMenuOnLinks: true,
  useShouldOverrideUrlLoading: true,
  javaScriptEnabled: true,
)

Stacktrace/Logs

I/flutter (21958): type 'Null' is not a subtype of type 'String'
I/flutter (21958): #0      AndroidInAppWebViewController._handleMethod (package:flutter_inappwebview_android/src/in_app_webview/in_app_webview_controller.dart:1412)
I/flutter (21958): #1      InternalChannelController.initMethodCallHandler.<anonymous closure> (package:flutter_inappwebview_platform_interface/src/util.dart:631)
I/flutter (21958): #2      MethodChannel._handleAsMethodCall (package:flutter/src/services/platform_channel.dart:607)
I/flutter (21958): #3      MethodChannel.setMethodCallHandler.<anonymous closure> (package:flutter/src/services/platform_channel.dart:597)
I/flutter (21958): #4      _DefaultBinaryMessenger.setMessageHandler.<anonymous closure> (package:flutter/src/services/binding.dart:663)
I/flutter (21958): #5      _invoke2 (dart:ui/hooks.dart:455)
I/flutter (21958): #6      _ChannelCallbackRecord.invoke (dart:ui/channel_buffers.dart:45)
I/flutter (21958): #7      _Channel.push (dart:ui/channel_buffers.dart:136)
I/flutter (21958): #8      ChannelBuffers.push (dart:ui/channel_buffers.dart:344)
I/flutter (21958): #9      PlatformDispatcher._dispatchPlatformMessage (dart:ui/platform_dispatcher.dart:822)
I/flutter (21958): #10     _dispatchPlatformMessage (dart:ui/hooks.dart:369)

Potential non-null String reads in flutter_inappwebview_android 1.2.0-beta.3:

String origin = call.arguments["origin"]; // onGeolocationPermissionsShowPrompt
String url = call.arguments["url"];       // onReceivedTouchIconUrl / onSafeBrowsingHit
String title = call.arguments["title"];   // onContextMenuActionItemClicked

Flutter version

3.44.0

Operating System, Device-specific and/or Tool

macOS 26.5.1 25F80 darwin-arm64
Android device: SM-F936N
Android version: 16
Android API level: 36
Android WebView: com.google.android.webview 149.0.7827.91
Android SDK: 37.0.0
Java: OpenJDK 21.0.8 bundled with Android Studio

flutter doctor -v reports no issues.

Plugin version

flutter_inappwebview: 6.2.0-beta.3

Additional information

This started after upgrading from the previous stable version:

flutter_inappwebview: 6.1.5
flutter_inappwebview_android: 1.1.3
flutter_inappwebview_platform_interface: 1.3.0+1

Current resolved package versions:

flutter_inappwebview: 6.2.0-beta.3
flutter_inappwebview_android: 1.2.0-beta.3
flutter_inappwebview_platform_interface: 1.4.0-beta.3

The same application did not show this error on flutter_inappwebview 6.1.5.

This may be a regression in the 6.2.0 beta line. The changelog for the 6.2.0 beta line includes platform interface/code generation/fromMap/toMap and Android dependency updates, so the native-to-Dart MethodChannel payload handling may need additional null safety guards.

Relevant changelog:
https://github.com/pichillilorenzo/flutter_inappwebview/blob/master/flutter_inappwebview/CHANGELOG.md#620-beta3

I am also trying to capture the exact MethodChannel event name by enabling PlatformInAppWebViewController.debugLoggingSettings.

Self grab

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