I'm try to edit my post using Laravel update but getting error

this is my html form

<form class="form-horizontal" action="" method="post">
            <input name="method" type="hidden" value="patch"/>
            <div class="form-group">
            <input name="_token" type="hidden" value=""/>

here is route:

Route::patch('blog/{id}','BlogController@update');

Controller :

public function update(Request $request,$id){
    $input = $request->all();
    $blog  =findOrFail($id);
    Blog::update($input);
    //var_dump($input);
    return back();
}

can you please show me where is the issue.

via Chebli Mohamed