samples/experimental/null_safety/null_safe_app/.vscode/launch.json

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "null_safe_app",
            "program": "lib/main.dart",
            "request": "launch",
            "type": "dart",
            "args": [
                "--enable-experiment=non-nullable",
            ],
        }
    ]
}