type 'Null' is not a subtype of type 'String' when packaging Windows app

[JaganGenji]

Hello FastForge team 👋,

I encountered an error while trying to package my Flutter Windows app using FastForge v0.6.6.
The build process successfully generates the .exe file, but fails during the packaging step with the following error:

type 'Null' is not a subtype of type 'String' #0 new MakeExeConfig.fromJson (package:flutter_app_packager/src/makers/exe/make_exe_config.dart:36:29) #1 MakeExeConfigLoader.load (package:flutter_app_packager/src/makers/exe/make_exe_config.dart:117:26) #2 FlutterAppPackager.package (package:flutter_app_packager/src/flutter_app_packager.dart:40:39) #3 UnifiedDistributor.package (package:unified_distributor/src/unified_distributor.dart:197:51) <asynchronous suspension> #4 CommandRunner.runCommand (package:args/command_runner.dart:212:13) <asynchronous suspension> #5 main (file:///C:/Users/genji/AppData/Local/Pub/Cache/hosted/pub.dev/fastforge-0.6.6/bin/main.dart:10:10) <asynchronous suspension>
### Environment Details:

OS | Windows 11
Flutter | 3.32.6 (stable)
FastForge | 0.6.6
Project Type | Flutter Windows app (Release build)

make_config.yaml Content:

display_name: "my app"
publisher_name: "Systems Pvt Ltd"
identity_name: "com.myapp.desktop"
version: "6.4.0.1"
architecture: "x64"
description: "myappdesktop app packaged with FastForge"
copyright: "© 2025 Systems Pvt Ltd"
publisher_url: "https://myapp.com"
license: "MIT"
icon_path: "windows/runner/resources/app_icon.ico"
output_path: "build/windows/x64/runner/Release/installer"

assets:

• "build/windows/x64/runner/Release/data/**"
• "build/windows/x64/runner/Release/ddls/**"

File location:

windows/packaging/exe/make_config.yaml
Expected Behavior:

FastForge should package the .exe successfully into the specified installer output path.

Actual Behavior:

The process throws a type 'Null' is not a subtype of type 'String' exception and exits before packaging.