Call to a member function middleware() on null

 In web.php I the following routes:

web.php

Route::prefix('app')->group(function(){

    Route::post('/create_tag','AdminController@addTag');

})->middleware(AdminCheck::class);

Here, middleware is AdminCheck.

and in my AdminCheck middleware I wrote the following to test the middleware:

AdminCheck.php 

public function handle($request, Closure $next)

    {

        if(!Auth::check())

        {

            return 'not loggedIn';

        }

        return $next($request);

    }

Now when I reload the '/' url of the website it shows 'Call to a member function middleware() on null' 

error.

To solve this: 

In web.php change the previous middleware position like the following:

Route::prefix('app')->middleware([AdminCheck::class])->group(function(){

    Route::post('/create_tag','AdminController@addTag');

});

and inside AdminCheck.php middleware do the following: 

public function handle($request, Closure $next)

    {

        

        if(!Auth::check())

        {

            return response()->json([

                'msg' => 'You are not allowed to access this route'

            ],402);

        }

        return $next($request);

    }