const-final.dart

void main() {
  var tmp = "tmp";
  final finalVar = tmp;
  // Const variables must be initialized with a constant value.
//   const constVar = tmp;
  const _constVar = "const";
  const constVar = _constVar;
  print(finalVar + constVar);
}

null.dart

void main() {  
  const Null nullVar = null; // type is Null
//   type(str);
  //str = "change";
  print(nullVar.runtimeType.toString());
  
  const String strVar = null;
  const int intVar = null;
  
  print(nullVar == strVar);
  print(intVar == nullVar);
  print(intVar == strVar);
  
  assert(false);
  
  List<int> nums = [1, 2, 3];
  //nums.add("4")
}