Grey screen with 'flutter run --release'

Hi.

I simply built a page with the text "Hello World" and a button located below the text, as shown in the figure below. The page was successfully published using a FlutterFlow domain. For some reason, I wish to host it using Firebase.

So, I used FlutterFlow desktop to export the code. I set up the Flutter SDK v3.22.2, which aligns with the FlutterFlow recommendation. Flutter doctor shows all green. The code was successfully downloaded, and flutter build web works perfectly. The page shows properly using --debug and --profile modes.

However, when I try to use --release, the Chrome browser only shows a grey screen. I tried to deploy using Firebase, and the result is the same - a grey screen. The browser console shows "Null check operator used on a null value", refer to figure below, which I have no idea about at all.