如果字段为空，如何提示消息，Laravel

use Illuminate\Http\Request;
use Illuminate\Support\Facades\Validator;

public function store(Request $request)
{
    $rules = [
        'field_name' => 'required',
    ];

    $messages = [
        'field_name.required' => '字段不能为空。',
    ];

    $validator = Validator::make($request->all(), $rules, $messages);

    if ($validator->fails()) {
        // 如果验证失败，将错误消息返回给用户
        return redirect()->back()->withErrors($validator)->withInput();
    }

    // 如果验证通过，执行其他操作
    // ...
}

@if ($errors->any())
    <div class="alert alert-danger">
        <ul>
            @foreach ($errors->all() as $error)
                <li>{{ $error }}</li>
            @endforeach
        </ul>
    </div>
@endif