non-null use after null check should not generate an error

main.dart

class A
{
  String? get startScriptPath => null;

  bool addToPath(String path) {
    if (startScriptPath != null) {
        if (!exists(startScriptPath)) {
          print('hi');
        }
    } else {
      throw UnsupportedError(
          "The shell oesn't support a start script so we can't configure the path");
    }
    return true;
  }
  
  bool exists(String path) => true;
}