Laravel教程-电商实战中创建商品出现TypeError

下面是报错

以下是控制器

    protected function form()
    {
        $form = new Form(new Product());

        $form->text('title', __('Title'))->rules('required');

        $form->quill('description', __('Description'))->rules('required');

        $form->image('image', __('Image'))->rules('required|image')->default('');

        $form->radio('on_sale', __('On sale'))->options(['1'=>'Yes','2'=>'No'])->default(1);

        $form->hasMany('skus','SKU Label',function (Form\NestedForm $form){
            $form->text('title','SKU Name')->rules('required');
            $form->text('description','SKU Description')->rules('required');
            $form->text('price','Unit Price')->rules('required|numeric|min:0.01');
            $form->text('stock','Stock')->rules('required|integer|min:0');
        });

        $form->saving(function (Form $form) {
            $form->model()->price = collect($form->input('skus'))->where(Form::REMOVE_FLAG_NAME, 0)->min('price') ?: 0;
        });

        return $form;
    }