我正在Laravel中写一段代码，当我尝试用表单中的文件发帖时，它会抛出以下异常：
得到错误'PHP消息：PHP致命错误：未捕获的错误异常：包括（/var/www/vhosts/web2/httpdocs/vendor/composer/../../app/Exceptions/Handler.php）：无法打开流：在/var/www/vhosts/web2/httpdocs/vendor/composer/ClassLoader中没有这样的文件或目录。php：444\n堆栈跟踪：\n#0

第5个/var/www/vhosts/web2/httpdocs/供应商/拉瑞维尔/框架/源代码/照明/容器/容器.php（803）：反射类-〉__构造（'App...'，引用对象：（隐藏）
add.blade.php:

@include('flash::message')
<form class="form-horizontal" enctype="multipart/form-data" action="{{action('SheetController@add')}}" method="post">
@csrf
<div class="form-group">
  <label class="col-md-4 control-label" for="icao">ICAO</label>  
  <div class="form-group col-md-4">
    <input placeholder="i.e. SAAC" class="form-control input-md" id="icao" name="icao" type="text" required />
  </div>
</div>

<div class="form-group">
  <label class="col-md-4 control-label" for="fir">FIR</label>  
  <div class="col-md-4">
    <select id="fir" name="fir" class="form-control input-md" required>
    <option value="SAEF">Ezeiza</option>
    <option value="SACF">C&oacute;rdoba</option>
    <option value="SAMF">Mendoza</option>
    <option value="SAVF">Comodoro Rivadavia</option>
    <option value="SARR">Resistencia</option>
   </select>
  </div>
</div>

<div class="form-group">
  <label class="col-md-4 control-label" for="version">Version</label>  
  <div class="form-group col-md-4">
    <input placeholder="i.e. 1.2" class="form-control input-md" id="version" name="version" type="text" required />
  </div>
</div>

<!-- File input-->
<div class="form-group">
  <label class="col-md-4 control-label" for="sheetfile">Archivo</label>  
  <div class="col-md-4">
    <input id="sheetfile" name="sheetfile" class="form-control input-md" required type="file">
  </div>
</div>

<hr style="margin-bottom:20px;">

<div class="form-group">
  <div class="btn-group">
    <button type="submit" class="btn btn-success">Add</button>
    <input type="reset" class="btn btn-warning" value="Reset" />
  </div>
</div>

</form>

SheetController.php:

public function add(Request $request)
{
    if(!empty($request->all()))
    {
        $sheet = new Sheet();
        $sheet->icao = $request->icao;
        $sheet->fir = $request->fir;
        $sheet->version = $request->version;

        $newName = $sheet->icao.'_v'.$sheet->version.'.pdf';

        if($request->file('sheetfile')->getClientOriginalExtension() != 'pdf')
        {
            flash()->error('File not allowed')->important();
        }
        else if($request->imagen->storeAs('ATC/Sheets', $newName, 'files'))
        {
            if($sheet->save()) flash()->success('Sheet added')->important();
            else flash()->error($sheet->errors()->first())->important();
        }
        else flash()->error('The file could not be uploaded.')->important();
    }
    return redirect()->action('SheetController@list');
}

我已经试过composer update和composer dump-autoload了
有什么想法吗？