我需要验证我的图像数组作为一个图像和特定的图像文件扩展名只。但是我对图像的请求验证不允许我使用inser null值
例如，我会添加一个内容，不想添加图像。然后图像应该包含null，这就是为什么我需要请求验证为null。但根据我的经验，空值是不允许的，它给了我一个错误，为什么？请帮帮我
这是错误。
未定义变量：升级
这是我的控制器

public function store(Request $request)
    {
        $this->validate($request, [
            'promotion_image' => 'image|nullable|max:1999'
        ]);

        if ($request->has('promotion_image'))
        {   
            //Handle File Upload

            $promotion = [];
            foreach ($request->file('promotion_image') as $key => $file)
            {
                // Get FileName
                $filenameWithExt = $file->getClientOriginalName();
                //Get just filename
                $filename = pathinfo( $filenameWithExt, PATHINFO_FILENAME);
                //Get just extension
                $extension = $file->getClientOriginalExtension();
                //Filename to Store
                $fileNameToStore = $filename.'_'.time().'.'.$extension;
                //Upload Image
                $path = $file->storeAs('public/promotion_images',$fileNameToStore);
                array_push($promotion, $fileNameToStore);
            }

            $fileNameToStore = serialize($promotion);
        }
        else
        {
            $fileNameToStore='noimage.jpg';
        }

        if (count($promotion)) {
            $implodedPromotion = implode(' , ', $promotion);
            $promotionImage = new Promotion;
            $promotionImage->promotion_image = $implodedPromotion;
            $promotionImage->save();

            return redirect('/admin/airlineplus/promotions')->with('success', 'Image Inserted');
        }

        return redirect('/admin/airlineplus/promotions')->with('error', 'Something went wrong.');

        }

这是我的观点

{!! Form::open(['action'=>'Admin\PromotionsController@store', 'method' => 'POST','enctype'=>'multipart/form-data', 'name' => 'add_name', 'id' => 'add_name']) !!}
<div class="form-group">   
    <div class="table-responsive">  
        <table class="table table-bordered" id="dynamic_field">  
           <tr>  
              <td> {{ Form::file('promotion_image[]')}}</td>

              <td>{{ Form::button('', ['class' => 'btn btn-success fa fa-plus-circle', 'id'=>'add','name'=>'add', 'style'=>'font-size:15px;']) }}</td>
           </tr>  
        </table>  
        {{Form::submit('submit', ['class'=>'btn btn-primary', 'name'=>'submit'])}}
    </div> 
</div>  
{!! Form::close() !!}