如何在TextFormField下面添加图标到errorText？

import 'package:flutter/material.dart';

class MyForm extends StatefulWidget {
  @override
  _MyFormState createState() => _MyFormState();
}

class _MyFormState extends State<MyForm> {
  final _formKey = GlobalKey<FormState>();
  String _name;

  @override
  Widget build(BuildContext context) {
    return Form(
      key: _formKey,
      child: Column(
        children: [
          Stack(
            children: [
              TextFormField(
                decoration: InputDecoration(
                  labelText: 'Name',
                ),
                validator: (value) {
                  if (value.isEmpty) {
                    return 'Please enter your name';
                  }
                  return null;
                },
                onSaved: (value) {
                  _name = value;
                },
              ),
              Positioned(
                right: 0,
                bottom: 0,
                child: Icon(
                  Icons.error,
                  color: Colors.red,
                ),
              ),
            ],
          ),
          RaisedButton(
            onPressed: () {
              if (_formKey.currentState.validate()) {
                _formKey.currentState.save();
                // 执行表单提交操作
              }
            },
            child: Text('Submit'),
          ),
        ],
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: Scaffold(
      appBar: AppBar(
        title: Text('Form Example'),
      ),
      body: MyForm(),
    ),
  ));
}