Laravel 5-验证为假时的MethodNotAllowedHttpException

总是在验证失败时，我得到MethodNotAllowedHttpException

routes.php

Route::post('download', 'UrlController@download');
Route::post('search', 'UrlController@search');

UrlController.php

public function download(DownloadRequest $request)
{
    dd($request->all());
}

DownloadRequest.php

public function authorize()
{
    return true;
}

 public function rules()
{
    return [
        'format' => 'required|between:1,13'
    ];
}

name.blade.php

{!! Form::open(['url' => 'download']) !!}

{!! Form::select('format', [
    'Please select format',
    'FormatGrp1' => [1 => 'best', 'p1','p2', 'p3', 'p4'],
    'FormatGrp2' => [6 => 'p5', 'p6']
]) !!}

当“请选择格式”选择并提交表单时，我总是得到这个错误，因为“请选择格式”有值0和我指定的值必须在1到13（看DownloadRequest.php）之间

感谢帮助！