Issue with OutlineInputBorder and DropdownButtonFormField: Button is not clickable due to decoration

main.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        appBar: AppBar(
          title: Text("Dropdown test"),
        ),
        body: Center(
          child: DropdownButtonFormField<String>(
            decoration: InputDecoration(
              border: OutlineInputBorder(),
              labelText: "Select option",
            ),
            items: ["1", "2", "3"]
                .map<DropdownMenuItem<String>>(
                  (option) => DropdownMenuItem<String>(
                    value: option,
                    child: Text(option),
                  ),
                )
                .toList(),
            onChanged: (val) {},
          ),
        ),
      ),
    );
  }
}