anchor.diff:    final Statement? initializer;
     final Expression? condition;
     final Expression? updater;
  -  final List<Statement> body;
  +  final Statement body;
     final bool forCollection;
   
     _For(this.initializer, this.condition, this.updater, this.body,
  
positive.code:     if (updater != null) {
        buffer.write(' $updater');
      }
      buffer.write(') ${block(body)}');
      return buffer.toString();
    }
  
  
negative.code:     Var variable, Expression iterable, List<Statement> body) {
    // ignore: unnecessary_null_comparison
    assert(variable != null);
    return new _ForEach(variable, iterable, block(body), false);
  }
  
  /// Creates a [Statement] that, when analyzed, will cause [callback] to be
  