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Kira-kira error kenapa ya padahal sudah benar semua tapi tetap saja error

Route : Web :

<?php

use App\Http\Controllers\SiswaController;
use Illuminate\Support\Facades\Route;

/*
|--------------------------------------------------------------------------
| Web Routes
|--------------------------------------------------------------------------
|
| Here is where you can register web routes for your application. These
| routes are loaded by the RouteServiceProvider within a group which
| contains the "web" middleware group. Now create something great!
|
*/

Route::get('/', function () {
    return view('home');
});

//Login
Route::get('/login','AuthController@login')->name('login');
Route::post('/post-login','AuthController@postlogin');
Route::get('/logout','AuthController@logout');

//Dashboard Admin
    Route::group(['middleware' => ['auth','CheckRole:admin']],function (){
    Route::get('/siswa','SiswaController@index');
    Route::post('/siswa/create','SiswaController@create');
    Route::get('/siswa/{siswa}','SiswaController@show');
    Route::get('/siswa/{siswa}/edit','SiswaController@edit');
    Route::post('/siswa/{id}/update','SiswaController@update');
    Route::delete('/siswa/{siswa}','SiswaController@destroy');
    Route::get('/siswa/addVal','SiswaController@addVal');
});

//Dashboard Siswa
Route::group(['middleware' => ['auth','CheckRole:admin,siswa']],function (){
    Route::get('/dashboard','DashboardController@index');
});

SiswaController :

<?php

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use Illuminate\Support\Str;
use App\Siswa;

class SiswaController extends Controller
{

    public function index(Request $request)
    {
        if($request->has('cari'))
        {
            $table = Siswa::where('kd_siswa','LIKE','%' . $request->cari . '%')->get();
        }else{
            $table = Siswa::all();
        }
        return view('siswa.index',compact('table'));

    }
    public function show(Siswa $siswa)
    {
        return view('siswa.show',compact('siswa'));

    }
    public function create(Request $request)
    {

        $request->validate([
            'nama_depan' => 'required',
            'kd_siswa' => 'required',
            'nama_belakang' => 'required',
            'jk' => 'required',
            'agama' => 'required',
            'alamat' => 'required'
            ]);

        //insert into table user
       $user = new \App\User;
       $user->role = 'siswa';
       $user->username = $request->nama_depan;
       $user->email = $request->email;
       $user->password = bcrypt('rahasia');
       $user->remember_token = Str::random(60);
       $user->save();

       //insert into table siswa
       $request->request->add(['user_id' => $user->id]);
       $siswa = Siswa::create($request->all());

       return redirect('/siswa')->with('sukses','Berhasil Input');
    }
    public function edit(Siswa $siswa)
    {
    //    $siswa =  Siswa::find($id);
        return view('siswa.edit',compact('siswa'));
    }
    public function update(Request $request,$id)
    {

        $siswa = Siswa::find($id);
        $siswa->update($request->all());
        if($request->hasFile('avatar'))
        {
            $request->file('avatar')->move('img',$request->file('avatar')->getClientOriginalName());
            $siswa->avatar = $request->file('avatar')->getClientOriginalName();
            $siswa->save();
        }
        return redirect('/siswa')->with('sukses','Berhasil update');
    }
    public function destroy(Siswa $siswa)
    {
        Siswa::destroy($siswa->id);
       return redirect('/siswa')->with('delete','Berhasil Hapus');
    }
    public function addVal()
    {
        return view('siswa.addVal');
    }
}

AddVal.blade.php :

@extends('layout.main')

@section('content')
@section('title','Data Siswa')
HALAMAN ADD NILAI
@endsection